Chapter XXI: Echinodermata (continued): Development and Phylogeny 601 (4)

Haeckel, in his Monograph of the Radiolaria of the _Challenger_ enumerated 739 genera, comprising 4318 species; and Dreyer has added 6 new genera, comprising 39 species, besides 7 belonging to known genera. Possibly, as we shall see, many of the species may be mere states of growth, for it is impossible to study the life-histories of this group; on the other hand, it is pretty certain that new forms are likely to be discovered and described. The Radiolaria are found living at all depths in the sea, by the superficial or deep tow-net; and some appear to live near the bottom, where the durable forms of the whole range also settle and accumulate. They thus form what is known as Radiolarian ooze, which is distinguished from other shallower deposits chiefly through the disappearance by solution of all calcareous skeletons, as they slowly fell through the waters whereon they originally floated at the same time with the siliceous remains of the Radiolaria. The greatest wealth of forms is found in tropical seas, though in some places in cold regions large numbers of individuals of a limited range of species have been found.

Radiolaria of the groups with a pure siliceous skeleton can alone be fossilised, even the impure siliceous skeleton of the Phaeodaria readily dissolving in the depths at which they live: they have been generally described by Ehrenberg's name _Polycystineae_. Tripolis (_Kieselguhr_) of Tertiary ages have been found in many parts of the globe, consisting largely or mainly of Radiolaria, and representing a Radiolarian ooze. That of the Miocene of Barbados contains at least 400 species; that of Gruppe at least 130. In Secondary and Palaeozoic rocks such oozes pass into Radiolarian quartzites (some as recent as the Jurassic). They occur also in fossilised excrement (coprolites), and in flint or chert concretions, as far down as the lowest fossiliferous rocks, {88}the Cambrian. The older forms are simple Sphaerellaria and Nassellaria. From a synopsis of the history of the order in Haeckel's _Monograph_ (pp. clxxxvi.-clxxxviii.) we learn that while a large number of skeletal forms had been described by Ehrenberg, Huxley in 1851 published the first account of the living animal. Since then our knowledge has been extended by the labours of Haeckel, Cienkowsky, R. Hertwig, Karl Brandt, and A. Borgert.

5. PROTEOMYXA

_Sarcodina without a clear ectoplasm, whose active forms are amoeboid or flagellate, or pass from the latter form to the former; multiplying chiefly, if not exclusively, by brood-formation in a cyst. No complete cell-pairing (syngamy) known, though the cytoplasms may unite into plasmodia; pseudopodia of the amoeboid forms usually radiate or filose, but without axial filaments. Saprophytic or parasitic in living animals or plants._

This group is a sort of lumber-room for forms which it is hard to place under Rhizopoda or Flagellata, and which produce simple cysts for reproduction, not fructifications like the Mycetozoa. The cyst may be formed for protection under drought ("hypnocyst"), or as a preliminary to spore-formation ("sporocyst"). The latter may have a simple wall (simple sporocyst), or else two or three formed in succession ("resting cyst"), so as to enable it to resist prolonged desiccation, etc.: both differing from the hypnocyst in that their contents undergo brood formation. On encystment any indigestible food materials are extruded into the cyst, and in the "resting cysts," which are usually of at least two layers, this faecal mass lies in the space between them. The brood-cells escape, either as flagellate-cells, resembling the simpler Protomastigina, called "flagellulae," and which often become amoeboid (Fig. 29); or already furnished with pseudopodia, and called "amoebulae," though they usually recall _Actinophrys_ rather than _Amoeba_. In _Vampyrella_ and some others the amoebulae fuse, and so attain a greater size, which is most probably advantageous for feeding purposes. But usually it is as a uninucleate cell that the being encysts. They may feed either by ingestion by the pseudopodia, by the whole surface contained in a living host-cell, or by passing a pseudopodium into a host-cell (Fig. 29 5). They may be divided as follows:—

{89}A. MYXOIDEA.—Flagella 1-3; zoospores separating at once.

1. ZOOSPOREAE.—Brood-cells escaping as flagellulae, even if they become
amoeboid later. _Ciliophrys_ Cienk.; _Pseudospora_ Cienk. (Fig. 29).

2. AZOOSPOREAE.—Cells never flagellate. _Protomyxa_ Haeckel;
_Plasmodiophora_ Woronin; _Vampyrella_ Cienk.; _Serumsporidium_ L.
Pfeiffer.

B. CATALLACTA.—Brood-cells of cyst on liberation adhering at the centre
to form a spherical colony, multiflagellate; afterwards separating, and
becoming amoeboid. _Magosphaera_ Haeckel (marine).[95]

_Plasmodiophora_ infests the roots of Crucifers, causing the disease known as "Hanburies," or "fingers and toes," in turnips, etc. _Serumsporidium_ dwells in the body cavity of small Crustacea. Many of this group were described by Cienkowsky under the name of "Monadineae" (in _Arch. Mikr. Anat._ i. 1865, p. 203). Zopf has added more than anyone else since then to our knowledge. He monographed them under Cienkowsky's name, as a subordinate group of the Myxomycetes, "_Pilzthiere oder Schleimpilze_," in Schenk's _Handb. d. Bot._ vol. iii. pt. ii. (1887). To Lankester (_Encycl. Brit._, reprint 1891) we owe the name here adopted. Zopf has successfully pursued their study in recent {90}papers in his _Beitr. Nied. Org._ The Chytridieae, usually ascribed to Fungi, are so closely allied to this group that Zopf proposes to include at least the Synchytrieae herein.

This group is very closely allied to Sporozoa; for the absence of cytogamy, and of sickle-germs,[96] and of the complex spores and cysts of the Neosporidia, are the only absolute distinctions.

6. MYCETOZOA (MYXOMYCETES, MYXOGASTRES)

_Sarcodina moving and feeding by pseudopodia, with no skeleton, aggregating more or less completely into complex "fructifications" before forming 1-nucleate resting spores; these may in the first instance liberate flagellate zoospores, which afterwards become amoeboid, or may be amoeboid from the first; zoospores capable of forming hypnocysts from which the contents escape in the original form._

1. Aggregation taking place without plastogamy, zoospores amoeboid, with
a clear ectosarc

ACRASIEAE.

_Copromyxa_ Zopf; _Dictyostelium_ Brefeld.

2. Aggregation remaining lax, with merely thread-like connexions, except
when encystment is to take place; cytoplasm finely granular throughout;
complete fusion of the cytoplasm doubtful

FILOPLASMODIEAE.

_Labyrinthula_ Cienk.; _Chlamydomyxa_ Archer; _Leydenia_ (?) Schaud.

3. Plasmodium formation complete, eventuating in the formation of a
complex fructification often traversed by elastic, hygroscopic threads,
which by their contraction scatter the spores; zoospores usually
flagellate at first

MYXOMYCETES.

_Fuligo_ Hall.; _Chondrioderma_ Rostaf.; _Didymium_ Schrad. (Fig. 30).

I. The ACRASIEAE are a small group of saprophytes, often in the most literal sense, though in some cases it has been proved that the actual food is the bacteria of putrefaction. In them, since no cell-division takes place in the fructification, it is certain that the multiplication of the species must be due to the fissions of the amoeboid zoospores, which often have the habit of _Amoeba limax_ (Fig. 1, p. 5).

II. FILOPLASMODIEAE.—_Chlamydomyxa_[97] is a not uncommon inhabitant of the cells of bog-mosses and bog-pools, and its nutrition may be holophytic, as it contains chromoplasts; but it {91}can also feed amoeba-fashion. _Labyrinthula_ is marine, and in its fructification each of the component cells forms four spores. _Leydenia_ has been found in the fluid of ascitic dropsy, associated with malignant tumour.

III. MYXOMYCETES.—The fructification in this group is not formed by the mere aggregation of the zoospores, but these fuse by their cytoplasm to form a multinucleate body, the "plasmodium," which, after moving and growing (with nuclear division) for some time like a great multinucleate Reticularian, passes into rest, and develops a fructification by the formation of a complex outer wall; within this the contents, after multiplication of the nuclei, resolve themselves into uninucleate spores, each with its own cyst-wall. The fructifications of this group are often conspicuous, and resemble those of the Gasteromycetous fungi (_e.g._, the Puffballs), whence they were at first called _Myxogastres_. De Bary first discovered their true nature in 1859, and ever since they have been claimed by botanist and zoologist alike.

The spore on germination liberates its contents as a minute flagellate, with a single anterior lash and a contractile vacuole (Fig. 30, C). It soon loses the lash, becomes amoeboid, and feeds on bacteria, etc. (Fig. 30, D, E). In this state it can pass into hypnocysts, from which, as from the spores, it emerges as a flagellula. After a time the amoeboids, which may multiply by fission, fuse on meeting, so as to form the plasmodium (Fig. 30, F). This contains numerous nuclei, which multiply as it grows, and numerous contractile vacuoles. When it attains full size it becomes negatively hydrotactic, crawls to a dry place, and resolves itself into the fructification. The external wall, and sometimes a basal support to the fruit, are differentiated from the outer layer of protoplasm; while the nuclei within, after undergoing a final bipartition, concentrate each around an independent portion of plasma, which again is surrounded as a spore by a cyst-wall. Often the maturing plasmodium within the wall of the fruit is traversed by a network of anastomosing tubes filled with liquid, the walls of which become differentiated into membrane like the fruit-wall, and are continuous therewith. As the fruit ripens the liquid dries, and the tubes now form a network of hollow threads, the "capillitium," often with external spiral ridges (Fig. 30, A, B). These are very hygroscopic, and by their expansion and contraction {92}determine the rupture of the fruit-wall and the scattering of the spores.

Again, in some cases the plasmodia themselves aggregate in the same way as the amoeboids do in the _Acrasieae_, and combine to form a compound fruit termed an "aethalium,"[98] with the regions of the separate plasmodia more or less clearly marked off. The species formerly termed _Aethalium septicum_ is now known as _Fuligo varians_. It is a large and conspicuous species, common on tan, and is a pest in the tanpits. Its aethalia may reach a {93}diameter of a foot and more, and a thickness of two inches. _Chondrioderma diffusum_, often utilised as a convenient "laboratory type," is common on the decaying haulms of beans in the late autumn. The interest of this group is entirely biological, save for the "flowers of tan."[99]

{94}CHAPTER IV

PROTOZOA (_CONTINUED_): SPOROZOA[100]

II. Sporozoa.

_Protozoa parasitic in Metazoa, usually intracellular for at least part
of their cycle, rarely possessing pseudopodia, or flagella (save in the
sperms), never cilia; reproduction by brood-formation, often of
alternating types; syngamy leading up to resting spores in which minute
sickle-germs are formed, or unknown (Myxosporidiaceae)._

This group, of which seven years ago no single species was known in its complete cycle, has recently become the subject of concentrated and successful study, owing to the fact that it has been recognised to contain the organisms which induce such scourges to animals as malarial fevers, and various destructive murrains. Our earliest accurate, if partial knowledge, was due to von Siebold, Kölliker, and van Beneden. Thirty years ago Ray Lankester in England commenced the study of species that dwell in the blood, destined to be of such moment for the well-being of man and the animals in his service; and since then our knowledge has increased by the labours of Manson, Ross and Minchin at home, Laveran, Blanchard, Thélohan, Léger, Cuénot, Mesnil, Aimé Schneider in France, Grassi in Italy, Schaudinn, Siedlecki, L. and R. Pfeiffer, Doflein in Central Europe, and many others.

{95}

As a type we will take a simple form of the highest group, the Gregarinidaceae, _Monocystis_, which inhabits the seminal vesicles of the earthworm. In its youngest state, the "sporozoite," it is a naked, sickle-shaped cell, which probably makes its way from the gut into one of the large radial cells of the seminal funnel, where it attains its full size, and then passes out into the vesicles or reservoirs of the semen, to lie among the sperm morulae and young spermatozoa. The whole interior is formed of the opaque endosarc, which contains a large central nucleus, and is full of refractive granules of paramylum or paraglycogen,[101] a carbohydrate allied to glycogen or animal starch, so common in the liver and {96}muscles of Metazoa; besides these it contains proteid granules which stain with carmine, and oil-drops. The ectosarc is formed of three layers: (1) the outer layer or "cuticle"[102] is, in many cases if not here, ribbed, with minute pores in the furrows, and is always porous enough to allow the diffusion of dissolved nutriment; (2) a clear plasmatic layer, the "sarcocyte"; (3) the "myocyte," formed of "myonemes," muscular fibrils disposed in a network with transverse meshes, which effect the wriggling movements of the cell. The endosarc contains the granules and the large central nucleus. The adult becomes free in the seminal vesicles; here two approximate, and surround themselves with a common cyst: a process which has received the name of "association" (Fig. 31, _g-i_). Within this, however, the protoplasms remain absolutely distinct. The nucleus undergoes peculiar changes by which its volume is considerably reduced. When this process of "nuclear reduction" is completed, each of the mates undergoes brood-divisions (_j_), so as to give rise to a large number of rounded naked 1-nucleate cells—the true pairing-cells. These unite two and two, and so form the 1-nucleate spores (_k-m_), which become oat-shaped, form a dense cyst-wall, and have been termed "pseudonavicellae" from their likeness to the Diatomaceous genus _Navicella_. Some of the cytoplasm of the original cells remains over unused, as "epiplasm," and ultimately degenerates, as do a certain number of the brood-cells which presumably have failed to pair. It is believed that the brood-cells from the same parent will not unite together. The contents of each spore have again undergone brood-division to form eight sickle-shaped zoospores, or "sporozoites" (_n-q_), and thus the developmental cycle is completed. Probably the spores, swallowed by birds, pass out in their excrement, and when eaten by an earthworm open in its gut; the freed sickle-germs can now migrate through the tissues to the seminal funnels, in the cells of which they grow, ultimately becoming free in the seminal vesicles.[103]

{97}We may now pass to the classification of the group.

A. TELOSPORIDIA.—Cells 1-nucleate until the onset of brood-formation,
which is simultaneous.

1. GREGARINIDACEAE.—Cells early provided with a firm pellicle and
possessing a complex ectosarc; at first intracellular, soon becoming
free in the gut or coelom of Invertebrates. Pairing between adults,
which simultaneously produce each its brood of gametes, isogamous or
bisexual, which pair within the common cyst; zygotospores surrounded by
a firm cyst, and producing within a brood of sickle-shaped zoospores.

(i.) SCHIZOGREGARINIDAE.—Multiplying by simple fission in the free
state as well as by brood-formation; the brood-cells conjugating in a
common cyst, but producing only one pairing nucleus in each mate (the
rest aborting), and consequently only one spore.

_Ophryocystis_ A. Schn.

(ii.) ACEPHALINIDAE.—Cell one-chambered, usually without an epimerite
for attachment.

_Monocystis_ F. Stein; _Lankesteria_ Mingazzini.

(iii.) DICYSTIDAE.—Cell divided by a plasmic partition; epimerite
usually present.

_Gregarina_ Dufour; _Stylorhynchus_ A. Schn.; _Pterocephalus_ A.
Schn.

2. COCCIDIACEAE.—Cells of simple structure, intracellular in Metazoa.
Pairing between isolated cells usually sexually differentiated as
oosphere and sperm, the latter often flagellate. Brood-formation of the
adult cell giving rise to sickle-shaped zoospores (merozoites), or
progamic and producing the gametes. Oosperm motile or motionless,
finally producing a brood of spores, which again give rise to a brood
of sickle-spores.

(i.) COCCIDIIDAE.—Cell permanently intracellular, or very rarely
coelomic, encysting or not before division; zoospores always
sickle-shaped; oosperm encysting at once, producing spores with a
dense cell-wall producing sickle-germs.

(ii.) HAEMOSPORIDAE.—Cells parasitic in the blood corpuscles or free
in the blood of cold-blooded animals, encysting before
brood-formation; zoospores sickle-shaped; oosperm at first motile.

_Lankeresterella_ Labbé; (_Drepanidium_ Lank.;) _Karyolysus_ Labbé;
_Haemogregarina_ Danilewski.

(iii.) ACYSTOSPORIDAE.—Cells parasitic in the blood and haematocytes
of warm-blooded Vertebrates; never forming a cyst-wall before
dividing; zoospores formed in the corpuscles, amoeboid. Gametocytes
only forming gametes when taken into the stomach of insects. Oosperm
at first active, passing into the coelom, producing naked spores
which again produce a large brood of sickle zoospores, which migrate
to the salivary gland, and are injected with the saliva into the
warm-blooded host.

_Haemamoeba_ Grassi and Feletti; _Laverania_ Grassi and Feletti;
_Haemoproteus_ Kruse; _Halteridium_ Labbé.[104]

B. NEOSPORIDIA.—Cells becoming multinucleate apocytes before any
brood-formation occurs. Brood-formation progressive through the apocyte,
not simultaneous.

{98}1. MYXOSPORIDIACEAE.—Naked parasites in cold-blooded animals.
Spore-formation due to an aggregation of cytoplasm around a single
nucleus to form an archespore, which then produces a complex of cells
within which two daughter-cells form the spores and accessory
nematocysts.

_Myxidium_ Bütsch.; _Myxobolus_ Bütsch.; _Henneguya_ Thélohan;
_Nosema_ Nageli (= _Glugea_ Th.).

2. ACTINOMYXIDIACEAE.[105]—Apocyte resolved into a sporange, containing
eight secondary sporanges (so-called spores), of ternary symmetry and
provided with three polar nematocysts.

3. SARCOSPORIDIACEAE.—Encysted parasites in the muscles of Vertebrates,
with a double membrane; spores simple.

_Sarcocystis_ Lankester.

_Monocystis_ offers us the simplest type of GREGARINIDACEAE. In most Gregarines (Figs. 31, 32) the sporozoite enters the epithelium-cell of the gut of an Arthropod, Worm or Mollusc, and as it enlarges protrudes the greater part of its bulk into the lumen, and may become free therein, or pass into the coelom. The attached part is often enlarged into a sort of grapple armed with spines, the "epimerite"; this contains only sarcocyte, the other layers being absent. The freely projecting body is usually divided by an ingrowth of the myocyte into a front segment ("protomerite"), and a rear one ("deutomerite"), with the nucleus usually in the latter. In this state the cell is termed a "cephalont." Conjugation is frequent, but apparently is not always connected with {99}syngamy or spore-formation; sometimes from two to five may be aggregated into a chain or "syzygy." The number of cases in which a syngamic process between two cells has been observed is constantly being increased. In _Stylorhynchus_ (Fig. 33) the conjugation at first resembles that of _Monocystis_, but the actual pairing-cells are bisexually differentiated into sperms in the one parent, and oospheres in the other; it is remarkable that here the pear-shaped sperms are apparently larger than the oospheres. In _Pterocephalus_ the chief difference is that the sperms are minute.[106] In all cases of spore-formation the epimerite is lost and the septum disappears; in this state the cell is termed a sporont. Sometimes the epiplasm of the sporont forms tubes ("sporoducts"), which project through the cyst-wall and give exit to the spores, as in _Gregarina_ (Fig. 32, C), a parasite in the beetle _Blaps_.

Gregarines infest most groups of Invertebrates except Sponges and perhaps Coelenterates, the only exception cited being that of _Epizoanthus glacialis_, a Zoantharian (p. 406). They appear to be relatively harmless and are not known to induce epidemics.

The COCCIDIACEAE never attain so high a degree of cellular differentiation as the Gregarines, which may be due to their habitat; for in the growing state they are intracellular parasites. Their life-history shows a double cycle, which has been most thoroughly worked out in COCCIDIIDAE by Schaudinn and Siedlecki in parasites of our common Centipedes. We take that of _Coccidium schubergi_ (in _Lithobius forficatus_[107]), beginning with the sporozoite, which is liberated from the spores taken in with the food, in the gut of the Centipede. This active sickle-shaped cell (Fig. 34, _l_) enters an epithelial cell of the mid-gut, and grows therein till it attains its full size (_a_), when it is termed a "schizont"; for it segments (Gk. σχίζω, "I split") superficially into a large number of sickle-shaped zoospores, the "merozoites" (_c_), resembling the sporozoites. The segmentation is superficial, so that there may remain a large mass of residual epiplasm. The merozoites are set free by the destruction of the epithelium-cell in which they were formed, and which becomes disorganised, like the residual epiplasm. Each merozoite may repeat the {100}behaviour of the sporozoite, so that the disease spreads freely, and becomes acute after several reinfections. After a time the adult parasites, instead of becoming schizonts and simply forming merozoites by division, differentiate into cells that undergo a binary sexual differentiation. Some cells, the "oocytes" (_d_, _e_), escape into the gut, and the nucleus undergoes changes by which some of its substance (or an abortive daughter-nucleus) is expelled to the exterior (_f_), such a cell is now an "oogamete" or oosphere. Others, again, are spermatogones (_h_): each when full grown on escaping into the gut commences a division (_i_, _j_), like that of the schizonts. The products of this division or segment-cells are the flagellate sperms (_s_): they are more numerous and more minute than the merozoites produced by the schizonts, and are attracted to the oosphere by chemiotaxy (p. 23), and one enters it and fuses with it (_g_). The oosperm, zygote or fertilised egg, thus formed invests itself with a dense cyst-wall, as a "oospore" (_k_), its contents form one or more (2, 4, 8, etc.) spores; and each spore forms again one, two, or four sickle-shaped zoospores ("sporozoites"), destined to be liberated for a fresh cycle of parasitic life when the spores are swallowed by another host.

{101}

In some cases the oogametes are at first oblong, like ordinary merozoites, and round off in the gut. The microgametocyte, or spermatogone, has the same character, but is smaller; it applies itself like a cap to one pole of the oogamete, which has rounded off; it then divides into four sperms, whose cytoplasm is not sharply separated; one of these then separates from the common mass, enters the oogamete, and so conjugation is effected, with an oosperm as its result. This latter mode of conjugation is that of _Adelea ovata_ and _Coccidium lacazei_: the former is probably the more primitive and the commoner. The sperms {102}of Coccidiidae, when free, usually possess two long flagella, either both anterior, or a very long one in front and a short one behind, both turned backwards.

The genus _Coccidium_ affects many animals, and one species in particular, _C. cuniculi_ Rivolta, attacks the liver of young rabbits,[108] giving rise to the disease "coccidiosis." _Coccidium_ may also produce a sort of dysentery in cattle on the Alpine pastures of Switzerland; and cases of human coccidiosis are by no means unknown. _Coccidium_-like bodies have been demonstrated in the human disease, "molluscum contagiosum," and the "oriental sore" of Asia; similar bodies have also been recorded in smallpox and vaccinia, malignant tumours and even syphilis, but their nature is not certainly known; some of these are now referred to Flagellata (see p. 121).

Closely allied to the Coccidiidae are the HAEMOSPORIDAE, dwellers in the blood of various cold-blooded Vertebrates,[109] and entering the corpuscles as sporozoites or merozoites to attain the full size, when they divide by schizogony; they are freed like those of the next family by the breaking up of the corpuscle. The merozoites were described by Gaule (1879) as "vermicles" ("Würmchen"), and regarded by him as peculiar segregation-products of the blood; though Lankester had described the same species in the Frog's blood as early as 1871, with a full recognition of its true character. His name, _Drepanidium_, has had to give way, having been appropriated to another animal, and has been aptly replaced by that of _Lankesterella_. The sexual process of _Karyolysus_ has been found to take place in a Tick, that of _Haemogregarina_ in a Leech, thus presenting a close analogy to the next group, which only differs in its less definite form in the active state, and in the lack of a cell-wall during brood-formation.

Laveran was the first to describe a member of the {103}ACYSTOSPORIDAE, in 1880, as an organism always to be found in the blood of patients suffering from malarial fever; this received the rather inappropriate name of _Plasmodium_, which, by a pedantic adherence to the laws of priority, has been used by systematists as a generic name. Golgi demonstrated the coincidence of the stages of the intermittent fever with those of the life-cycle of the parasite in the patient, the maturation of the schizont and liberation of the sporozoites coinciding with the fits of fever. Manson, who had already shown that the Nematodes of the blood that give rise to Filarial haematuria (see Vol. II. p. 149) have an alternating life in the gnats or mosquitos of the common genus _Culex_,[110] in 1896 suggested to Ronald Ross that the same might apply to this parasite, and thus inspired a most successful work. The hypothesis had old prejudices in its favour, for in many parts there was a current belief that sleeping under mosquito-netting at least helped other precautions against malaria. Ross found early in his investigations that _Culex_ was a good host for the allied genus _Haemoproteus_ or _Proteosoma_, parasitic in birds, but could neither inoculate man with fever nor be inoculated from man. He found, however, that the malaria germs from man underwent further changes in the stomach of a "dappled-wing mosquito," that is, as we have since learned, a member of the genus _Anopheles_. Thenceforward the study advanced rapidly, and a number of inquirers, including Grassi, Koch, MacCallum (who discovered the true method of sexual union in _Halteridium_[111]), and Ross himself, completed his discovery by supplying a complete picture of the life-cycles of the malaria-germs. Unfortunately, there has been a most unhappy rivalry as to the priority of the share in each fragment of the discovery, whose history is summarised by Nuttall, we believe, with perfect fairness.[112]

The merozoite is always amoeboid, and in this state enters the blood corpuscle; herein it attains its full size, as a schizont, becoming filled with granules of "melanin" or black pigment, probably a decomposition product of the red colouring matter (haemoglobin).

{104}

The nucleus of the schizont now divides repeatedly, and then the schizont segments into a flat brood of germs (merozoites), relatively few in the parasite of quartan fever (_Haemamoeba malariae_, Fig. 35, E-G), many in that of tertian (_H. vivax_, Fig. 35, M). These brood-cells escape and behave for the most part as before. But after the disease has persisted for some time we find that in the genus _Haemamoeba_, {105}which induces the common malarial fevers of temperate regions, certain of the full-grown germs, instead of behaving as schizonts, pass, as it were, to rest as round cells; while in the allied genus _Laverania_, (_Haemomenas_, Ross) these resting-cells are crescentic, with blunt horns, and are usually termed half-moons (Fig. 35, O, T), characteristic of the bilious or pernicious remittent fevers of the tropics and of the warmer temperate regions in summer. These round or crescent-shaped cells are the gametocytes, which only develop further in the drawn blood, whether under the microscope, protected against evaporation, or in the stomach of the _Anopheles_: the crescents become round, and then they, like the already round ones of _Haemamoeba_, differentiate in exactly the same way as the corresponding cells of _Coccidium schubergi_. The female cell only exhibits certain changes in its nucleus to convert it into an oosphere: the male emits a small number of sperms, long flagellum-like bodies, each with a nucleus; and these, by their wriggling, detach themselves from the central core, no longer nucleated. The male gametogonium with its protruded sperms was termed the "_Polymitus_ form," and was by some regarded as a degeneration-form, until MacCallum discovered that a "flagellum" regularly undergoes sexual fusion with an oosphere in _Halteridium_, as has since been found in the other genera. The oosperm (Y) so formed is at first motile ("ookinete"), as it is in Haemosporidae, and passes into the epithelium of the stomach of the gnat and then through the wall, acquiring a cyst-wall and finally projecting into the coelom (_a-e_). Here it segments into a number of spheres ("zygotomeres" of Ross) corresponding to the Coccidian spores, but which never acquire a proper wall (_f_). These by segmentation produce at their surface an immense quantity of elongated sporozoites (the "zygotoblasts" or "blasts" of Ross, Fig. 35, _g_), these are ultimately freed by the disappearance of the cyst-wall of the oosperm, pass through the coelom into the salivary gland (_h_), and are discharged with its secretion into the wound that the gnat inflicts in biting. In the blood the blasts follow the ordinary development of merozoites in the blood corpuscle, and the patient shows the corresponding signs of fever. This has been completely proved by rearing the insect from the egg, feeding it on the blood of a patient in whose blood there were ascertained to be the germs of a definite species of {106}_Haemamoeba_, sending it to England, where it was made to bite Dr. Manson's son, who had never had fever and whose blood on repeated examination had proved free from any germs. In the usual time he had a well-defined attack of the fever corresponding to that germ, and his blood on examination revealed the _Haemamoeba_ of the proper type. A few doses of quinine relieved him of the consequences of his mild martyrdom to science. Experiments of similar character but of less rigorous nature had been previously made in Italy with analogous results. Again, it has been shown that by mere precautions against the bites of _Anopheles_, and these only, all residents who adopted them during the malarious season in the most unhealthy districts of Italy escaped fever during a whole season; while those who did not adopt the precautions were badly attacked.[113]

_Anopheles_ flourishes in shallow puddles, or small vessels such as tins, etc., the pools left by dried-up brooks and torrents, as well as larger masses of stagnant water, canals, and slow-flowing streams. Sticklebacks and minnows feed freely on the larvae and keep down the numbers of the species; where the fish are not found, the larvae may be destroyed by pouring paraffin oil on the surface of the water and by drainage. A combination of protective measures in Freetown (Sierra Leone) and other ports on the west coast of Africa, Ismailia, and elsewhere, has met with remarkable success during the short time for which it has been tried; and it seems not improbable, that as the relatively benign intermittent fevers have within the last century been banished from our own fen and marsh districts, so the Guinea coast may within the next decade lose its sad title of "The White Man's Grave."

So closely allied to this group in form, habit, and life-cycle are some species of the Flagellate genus _Trypanosoma_, that in their less active states they have been unhesitatingly placed here (see p. 119). Schaudinn has seen Trypanosomic characters in the "blasts" of this group, which apparently is the most primitive of the Sporozoa and a direct offshoot of the Flagellates.

The MYXOSPORIDIACEAE (Fig. 36) are parasitic in various {107}cold-blooded animals. They are at least binucleate in the youngest free state, and become large and multinucleate apocytes, which may bud off outgrowths as well as reproduce by spores. The spores of the apocyte are not produced by simultaneous breaking up, but by successive differentiation. A single nucleus aggregates around itself a limited portion of the cytoplasm, and this again forms a membrane, becoming an archespore or a "pansporoblast," destined to produce two spores; within this, nuclear division takes place so as to form about eight nuclei, two of which are extruded as abortive, and of the other six, three are used up in the formation of each of the two spores. Of these three nuclei in each spore, two form nematocysts, like those of a Coelenterate (p. 246 f.), at the expense of the surrounding plasm; while the third nucleus divides to form the two final nuclei of the reproductive body. The whole aggregate of the reproductive body and the two nematocysts is enveloped in a bivalve shell. In what we may call germination, the nematocysts eject a thread that serves for attachment, the valves of the shell open, and the binucleate mass crawls out and grows afresh. _Nosema bombycis_ Nägeli (the spore of which has a single nematocyst) is the organism of the "Pébrine" of the silkworm, which was estimated to have caused a total loss in France of some £40,000,000 before Pasteur investigated the malady and prescribed the effectual cure, or rather precaution against its spread. This consisted in crushing each mother in water after it had laid its eggs and seeking for pébrine germs. If the mother proved to be infected, her eggs were destroyed, as the eggs she had laid were certain to be also tainted. Balbiani completed the study of the organism from a morphological standpoint. Some Myxosporidiaceae produce destructive epidemics in fish.

{108}The DOLICHOSPORIDIA or SARCOSPORIDIACEAE are, in the adult state, elongated sacs, often found in the substance of the voluntary muscles, and known as "Rainey's" or "Miescher's Tubes"; they are at first uninucleate, then multinucleate, and then break up successively into uninucleate cells, the spores, in each of which, by division, are formed the sickle-shaped zoospores.[114]

{109}CHAPTER V

PROTOZOA (_CONTINUED_): FLAGELLATA

III. Flagellata.

_Protozoa moving (and feeding in holozoic forms) by long flagella:
pseudopodia when developed usually transitory: nucleus single or if
multiple not biform: reproduction occurring in the active state and
usually by longitudinal fission, sometimes alternating with
brood-formation in the cyst or more rarely in the active state: form
usually definite: a firm pellicle or distinct cell-wall often present._

The Flagellates thus defined correspond to Bütschli's group of the Mastigophora. The lowest and simplest forms, often loosely called "Monads," are only distinguishable from Sarcodina (especially Proteomyxa) and Sporozoa by the above characters: their artificial nature is obvious when we remember that many of the Sarcodina have a flagellate stage, and that the sperms of bisexual Sporozoa are flagellate (as are indeed those of all Metazoa except Nematodes and most Crustacea). Even as thus limited the group is of enormous extent, and passes into the Chytridieae and Phycomycetes Zoosporeae on the one hand, and by its holophytic colonial members into the Algae, on the other.[115]

CLASSIFICATION.

A. Fission usually longitudinal (transverse only in a cyst), or if
multiple, radial and complete: pellicle absent, thin, or if armour-like,
with not more than two valves.

I. Food taken in at any part of the body by pseudopodia

1. PANTOSTOMATA

_Multicilia_ Cienk.; _Mastigamoeba_ F. E. Sch. (Fig. 37, 4).

{110}II. Food taken in at a definite point or points, or by absorption,
or nutrition holophytic.

1. No reticulate siliceous shell. Diameter under 500 µ (1/50").

* Contractile vacuole simple (one or more).

(α) Colourless: reserves usually fat: holozoic, saprophytic or
parasitic

2. PROTOMASTIGACEAE

(β) Plastids yellow or brown: reserves fat or proteid: nutrition
variable: body naked, often amoeboid in active state (_C. nudae_),
or with a test, sometimes containing calcareous discs
("coccoliths," "rhabdoliths") of peculiar form (_C. loricatae_)

3. CHRYSOMONADACEAE

_Chromulina_ Cienk.; _Chrysamoeba_ Klebs; _Hydrurus_ Ag.
_Dinobryon_ Ehrb. (Fig. 37, 11); _Syncrypta_ Ehrb. (Fig. 37, 12);
_Zooxanthella_ Brandt; _Pontosphaera_ Lohm.; _Coccolithophora_
Lohm.; _Rhabdosphaera_ Haeck.

(γ) Green, (more rarely yellow or brown) or colourless: reserves
starch: fission longitudinal

4. CRYPTOMONADACEAE

_Cryptomonas_ Ehrb. (Fig. 37, 9); _Paramoeba_ Greeff.

(δ) Green (rarely colourless): fission multiple, radial

5. VOLVOCACEAE

** System of contractile vacuoles complex, with accessory formative
vacuoles or reservoir, or both.

(ε) Pellicle delicate or absent: pseudopodia often emitted:
excretory pore distinct from flagellar pit: reserves fat

6. CHLOROMONADACEAE

_Chloramoeba_ Lagerheim; _Thaumatomastix_, Lauterborn.

(ζ) Pellicle dense, tough or hard, often wrinkled or striate:
contractile vacuole discharging by the flagellar pit. Nutrition
variable

7. EUGLENACEAE

_Euglena_ Ehrb.; _Astasia_ Duj. (Fig. 37, 3); _Anisonema_ Duj.;
_Eutreptia_ Perty (Fig. 42, p. 124); _Trachelomonas_ Ehrb. (Fig.
37, 1); _Cryptoglena_ Ehrb.

2. Skeleton an open network of hollow siliceous spicules. Plastids
yellow. Diameter under 500 µ.

8. SILICOFLAGELLATA

_Dictyocha_ Ehrb.

3. Diameter over 500 µ. Mouth opening into a large reticulate
endoplasm: flagella 1, or 2, very unequal.

9. CYSTOFLAGELLATA

_Noctiluca_ Suriray (Fig. 48); _Leptodiscus_ R. Hertw.

B. Fission oblique or transverse: flagella two, dissimilar, the one
coiled round the base of the other or in a traverse groove; pellicle
often dense, of numerous armour-like plates

10. DINOFLAGELLATA

_Ceratium_ Schrank; _Gymnodinium_ Stein; _Peridinium_ Ehrb. (Fig. 46);
_Pouchetia_ Schütt; _Pyrocystis_ Murray (Fig. 47); _Polykrikos_ Bütschli.

The Protomastigaceae and Volvocaceae are so extensive as to require further subdivision.

PROTOMASTIGACEAE

I. Oral spots 2. Flagella distant in pairs. DISTOMATIDAE

II. Oral spot 1 or 0.

{111}A. Flagellum 1.

(_a_) No anterior process: often parasitic

OIKOMONADIDAE

_Oikomonas_ K. (Figs. 37, 2, 8); _Trypanosoma_ Gruby (Fig. 39, _a-f_);
_Treponema_ Vuill. (Fig. 39, _g-i_).

(_b_) Anterior process unilateral or proboscidiform: cell often thecate

BICOECIDAE

_Bicoeca_ Clark; _Poteriodendron_ St.

(_c_) Anterior process a funnel, surrounding the base of the flagellum:
cells often thecate.

(i.) Funnel free

CRASPEDOMONADIDAE

_Codosiga_ Clark; _Monosiga_ Cl.; _Polyoeca_ Kent; _Proterospongia_
Kent; _Salpingoeca_ Cl.

(ii.) Funnel not emerging from the general gelatinous investment

PHALANSTERIDAE

B. Flagella 2, unequal or dissimilar in function, the one sometimes short
and thick.

(_a_) Both flagella directed forwards

MONADIDAE

_Monas_ St.; _Anthophysa_ Bory (Fig. 37, 13).

(_b_) One flagellum, usually the longer, turned backwards

BODONIDAE

_Bodo_ St. (Fig. 38).

C. Flagella 2, equal and similar

AMPHIMONADIDAE

_Amphimonas_ Duj.; _Diplomita_ K. (Fig. 37, 10); _Rhipidodendron_ St.
(Fig. 37, 14).

D. Flagella 3

TRIMASTIGIDAE

_Dallingeria_ K. (Fig. 37, 6); _Costia_ Leclercq.

E. Flagella 4 or more: mostly parasitic in Metazoa

POLYMASTIGIDAE

_Trichomonas_ Donne; _Tetramitus_ Perty (Fig. 37, 7); _Hexamitus_ Duj.;
_Lamblia_ Blanchard.

F. Flagella numerous, sometimes constituting a complete ciliiform
investment, and occasionally accompanied by an undulating membrane:
parasitic in Metazoa.

(_a_) Flagella long: nucleus single: parasitic in insects

TRICHONYMPHIDAE

_Dinenympha_ Leidy; _Joenia_ Grassi; _Pyrsonympha_ Leidy;
_Trichonympha_ Leidy; _Lophomonas_ St.; _Maupasia_ Schew.

(_b_) Flagella short, ciliiform, uniformly distributed: nuclei very
numerous, all similar: parasitic in Amphibia

OPALINIDAE

_Opalina_ Purkinje and Valentin (Fig. 41).

VOLVOCACEAE

A. Cells usually isolated, separating after fission or brood-formation.
Usually green (sometimes red), more rarely colourless saprophytes

CHLAMYDOMONADIDAE

_Chlamydomonas_ Ehrb.; _Phacotus_ Perty; _Polytoma_ Ehrb.; _Sphaerella_
Sommerf. (Fig. 43); _Zoochlorella_.

B. Cells multiplying in the active state by radial divisions in the same
plane and usually incurving to form a spherical colony, united in a
gelatinous investment, sometimes traversed by plasmic threads

VOLVOCIDAE

_Gonium_ O.F.M.; _Eudorina_ Ehrb.; _Pandorina_ Bory (Fig. 45);
_Stephanosphaera_ Cohn; _Volvox_ L. (Fig. 44).

{112}; in 8 are shown two stages in the ingestion of a food particle (_f_); _chr_, plastoids; _c.vac_, contractile vacuole; _f_, food particle; _g_, gullet; _l_, theca; _nu_, nucleus; _p_, protoplasm; _per_, peristome; _v.i_, vacuole of ingestion. (From Parker and Haswell, mostly from Bütschli's _Protozoa_.)]

{113}The modes of nutrition are threefold: the simplest forms live in liquids containing decaying organic matter which they absorb through their surface ("saprophytic"): others take in food either _Amoeba_ fashion, or into a vacuole formed for the purpose, or into a definite mouth ("holozoic"): others again have coloured plastids, green or brown or yellow ("holophytic"), having the plant's faculty of manufacturing their own food-supply. But we meet with species that show chromatophores at one time and lack them at another; or, again, the same individual (_Euglena_) may pass from holozoic life to saprophytic (_Paramoeba_, some Dinoflagellates) as conditions alter.

Many secrete a stalk at the hinder end: by "continuous" formation of this, without rupture at fission, a branching colony is formed (_Polyoeca_). This stalk may have a varying consistency. In _Anthophysa_ (Fig. 37, 13) it appears to be due to the welding of excrementitious particles voided at the hinder end of the body with a gelatinous excretion; but the division of the stalk is here occasional or intermittent, so that the cells are found in tufts at the apex of the branches. A corresponding secretion, gelatinous or chitinous, around the body of the cell forms a cup or "theca," within which the cell lies quite free or sticking to it by its surface, or attached to it by a rigid or contractile thread. The theca, again, may assume the form of a mere gelatinous mass in which the cell-bodies may be completely plunged, so that only the flagella protrude, as in Volvocidae, _Proterospongia_ (Fig. 75, p. 182), and _Rhipidodendron_ (Fig. 37, 14). Often this jelly assumes the form of a fan (_Phalansterium_), the branching tubes of which it is composed lying for some way alongside, and ultimately diverging. In _Hydrurus_, the branching jelly assumes the form of a branching Confervoid.[117]

The cell-body may be bounded by an ill-defined plasmatic layer in Chrysomonadaceae and some Protomastigaceae,[118] or it may form a plasmatic membrane or "pellicle," sometimes very firm and tough, or striated as in Euglenaceae, or it may have a separate "cuticle" (in the holophytic species formed of cellulose), or even a bivalve or multivalve shell of distinct plates, hinged or overlapping (_Cryptoglena_, _Phacotus_, Dinoflagellates). The wall of the {114}Coccolithophoridae, a family of Chrysomonadaceae, is strengthened by embedded calcareous spicules ("coccoliths," "cyatholiths," "rhabdoliths"), which in the most complex forms (cyatholiths) are like a shirt-stud, traversed by a tube passing through the stem and opening at both ends. These organisms[119] constitute a large proportion of the plankton; the spicules isolated, or in their original state of aggregation ("coccospheres," "rhabdospheres"), enter largely into the composition of deep-sea calcareous oozes. They occur fossil from Cambrian times (Potsdam sandstone of Michigan and Canada), and are in some strata extremely abundant, 800,000 occurring to the mm. cube in an Eocene marl.

The Silicoflagellates have siliceous skeletons resembling that of many _Radiolaria_, to which they were referred until the living organism was described (see pp. 79, 86 f.).

The flagellum has been shown by Fischer to have one of two forms: either it is whip-like, the stick, alone visible in the fresh specimen, being seen when stained to be continued into a long lash, hitherto invisible; or the whole length is fringed with fine ciliiform lateral outgrowths. If single it is almost always protruded as a tugging organ ("tractellum");[120] the chief exceptions are the Craspedomonads, where it is posterior and acts as a scull ("pulsellum"), and some Dinoflagellates, where it is reversible in action or posterior. In addition to the anterior flagellum there may be one or more posterior ones, which trail behind as sense organs, or may anchor the cell by their tips. _Dallingeria_ has two of these, and _Bodo saltans_ a single anterior anchoring lash, by which they spring up and down against the organic débris among which they live, and disintegrate it. The numerous similar long flagella of the Trichonymphidae afford a transition in the genus _Pyrsonympha_ to the short abundant cilia of _Opalina_, usually referred to the Ciliate Infusoria.

{115}An undulating membrane occurs, sometimes passing into the flagellum in certain genera, all parasitic, such as _Trypanosoma_ (incl. _Herpetomonas_), _Trichomonas_, _Hexamitus_, and _Dinenympha_.

In some cases the flagellum (or flagella) is inserted into a definite pit, which in allied forms is the mouth-opening. The contractile vacuole is present in the fresh-water forms, but not in all the marine ones, nor in the endoparasites. It may be single or surrounded by a ring of minute "formative" vacuoles or discharge into a permanently visible "reservoir." This again may discharge directly to the surface or through the pit or canal in which the flagellum takes origin (_Euglena_).

The "chromatophore" may be a single or double plate, or multiple.[121] In the peculiar form _Paramoeba_ the chromatophore may degenerate and be reproduced anew. It often encloses rounded or polygonal granules of uncoloured plasma, very refractive, known as "pyrenoids." These, like the chromatophores, multiply by direct fission. The "reserves" may be (1) fat-globules; (2) granules of a possibly proteid substance termed "leucosin"; (3) a carbohydrate termed "paramylum," differing slightly from starch (see p. 95); (4) true starch, which is usually deposited in minute granules to form an investment for the pyrenoid when such is present.

A strongly staining granule is usually present in the plasma near the base of the flagellum. This we may term a "blepharoplast" or a "centrosome" in the wider sense.

FISSION is usually longitudinal in the active state; a few exceptions are recorded. Encystment is not uncommon; and in the coloured forms the cyst-wall is of cellulose. Division in the cyst is usually multiple;[122] in the coloured forms, however, vegetative growth often alternates with division, giving rise to plant-like bodies. _Polytoma_ and other Chlamydomonadidae multiply by "brood-formation" in the active state; the blepharoplast, as Dangeard suggests, persisting to continue the motion of the flagella of the parent, while the rest of the plasm divides to form the brood. CONJUGATION has been observed in many species. In some species of _Chlamydomonas_ it takes place after one or both of the two {116}cells have come to rest, but in most cases it occurs between active cells. We find every transition between equal unions and differentiated sexual unions, as we shall see in discussing the Volvocaceae.[123] The "coupled-cell" differs in behaviour in the different groups, but almost always goes to rest and encysts at once, whatever it may do afterwards.

The LIFE-HISTORY of many Flagellates has been successfully studied by various observers, and has shed a flood of light on many of the processes of living beings that were hitherto obscure. The first studies were carried through by the patient labours of Drysdale and Dallinger. A delicate mechanical stage enabled the observer to keep in the field of view a single Flagellate, and, when it divided into two, to follow up one of the products. A binocular eye-piece saved much fatigue, and enabled the observers to exchange places without losing sight of the special Flagellate under observation; for the one who came to relieve would put one eye to the instrument and recognise the individual Flagellate under view as he passed his hand round to the mechanism of the stage before the first watcher finally relinquished his place at the end of the spell of work. Spoon-feeding by Mrs. Dallinger enabled such shifts to be prolonged, the longest being one of nine hours by Dr. Dallinger.

{117}

The life-cycles varied considerably in length. It was in every case found that after a series of fissions the species ultimately underwent conjugation (more or less unequal or bisexual in character);[124] the zygote encysted; and within the cyst the protoplasmic body underwent brood-formation, the outcome of which was a mass of {118}spores discharged by the rupture of the cyst (Fig. 38). These spores grow from a size too minute for resolution by our microscopes into the ordinary flagellate form. They withstand the effects of drying, if this be effected immediately on their escape from the ruptured cyst; so that it is probable that each spore has itself a delicate cyst-wall and an aplanospore, from which a single zoospore escapes. The complex cycle, of course, comprises the whole course from spore-formation to spore-formation. Such complete and regular "life-histories," each characteristic of the species, were the final argument against those who held to the belief that spontaneous generation of living beings took place in infusions of decomposing organic matter.

Previous to the work of these observers it had been almost universally believed that the temperature of boiling water was adequate to kill all living germs, and that any life that appeared in a closed vessel after boiling must be due to spontaneous change in its contents. But they now showed that, while none of the species studied resisted exposure _in the active condition_ to a temperature of 138°-140° F., the spores only succumbed, in liquid, to temperatures that might even reach 268° F., or when dry, even 300° F. or more. Such facts explain the constant occurrence of one or more such minute species in liquids putrefying under ordinary conditions, the spores doubtless being present in the dust of the air. Very often several species may co-exist in one infusion; but they separate themselves into different zones, according to their respective need for air, when a drop of the liquid is placed on the slide and covered for examination. Dallinger[125] has made a series of experiments on the resistance of these organisms in their successive cycles to a gradual rise of temperature. Starting with a liquid containing three distinct species, which grew and multiplied normally at 60° F., he placed it under conditions in which he could slowly raise the temperature. While all the original inmates would have perished at 142° F., he succeeded in finally producing races that throve at 158° F., a scalding heat, when an accident put an end to that series of experiments. In no instance was the temperature raised so much as to kill off the beings, so that the increased tolerance of their descendants was due not, as might have been anticipated, to selection of those that best resisted, but to the inheritance of {119}an increased toleration and resistance from one generation or cycle to another.

As we noted above (p. 40), the study of the Flagellates has been largely in the hands of botanists. After the work of Bütschli in Bronn's _Thier-Reich_, Klebs[126] took up their study; and the principal monographs during the last decade have appeared in Engler and Prantl's _Pflanzenfamilien_, where Senn[127] treats the Flagellates generally, Wille[128] the Volvocaceae, and Schütt the "Peridiniales" or Dinoflagellata;[129] while only the Cystoflagellata, with but two genera, have been left to the undisputed sway of the zoologists.[130]

Among this group the majority are saprophytes, found in water containing putrefying matter or bacteria. The forms so carefully studied by Dallinger and Drysdale belong to the genera _Bodo_, _Cercomonas_, _Tetramitus_, _Monas_, and _Dallingeria_. Many others are parasites in the blood or internal cavities of higher animals, some apparently harmless, such as _Trichomonas vaginalis_, parasitic in man, others of singular malignity. _Costia necatrix_, infesting the epithelial scales of fresh-water fish, often devastates hatcheries. The genus _Trypanosoma_, Gruby, contributes a number of parasites, giving rise to deadly disease in man and beast.[131] _T. lewisii_ is common in Rodents, but is relatively harmless. _T. evansii_ is the cause of the Surra disease of Ruminants in India, and is apparently communicated by the bites of "large brown flies" (almost certainly Breeze Flies or Tabanidae, Vol. VI. p. 481). _T. brucei_, transferred to cattle by the Tsetse Fly, _Glossina morsitans_ (see Vol. VI. Fig. 244, p. 513) in Equatorial Africa, is the cause of the deadly Nagana disease, which renders whole tracts of country impassable to ox or horse. Other Trypanosomic diseases of animals are, in Algeria and the Punjab, "dourine," infecting horses and dogs; in South America, Mal de Caderas (falling-sickness), an epidemic paralysis of cattle. During the printing of this book, much additional knowledge has been gained on this genus and the diseases it engenders. The Trypanosomic {120}fever recently recognised on the West Coast has been found to be the early stage of the sleeping-sickness, that well-known and most deadly epidemic of Tropical Africa. Through the researches of Castellani, Nabarro, and especially Colonel and Mrs. Bruce, we know now that the parasite _T. gambiense_ is transferred by an intermediate host, a kind of Tsetse Fly (_Glossina palpalis_). Schaudinn's full study of a parasite of the blood corpuscles of the Owl has shown that while in its intracorpuscular state it resembles closely the malarial parasites in behaviour, and in its schizogenic multiplication, so that it was considered an Acystosporidian, under the name of _Halteridium_, it is really a _Trypanosoma_;[132] for the accomplishment of successful sexual reproduction it requires transference to the gut of a gnat (_Culex_). The germs may infect the ovary, and give the offspring of the insect the innate power of infecting Owls. Thus a new light is shed on the origin of the Coccidiaceae, whose "blasts" in the insect host resemble _Trypanosoma_ in their morphology.

The human Tick fever of the Western United States and the epizootic Texas fever are known to be due to blood parasites of the genus _Piroplasma_ (_Babesia_), of which the free state is that of a Trypanosome. It appears certain that Texas fever, though due to Tick bites, is not transferred directly from one beast to another by the same Tick; but the offspring of a female Tick that has sucked an infected ox contains Trypanosome germs, and will by their bites infect other animals. {121}It would seem probable that the virulence of the Persian Tick (_Argas persica_) is due to similar causes. The Indian maladies known as "Kala Azar" and "Oriental Sore" are characterised by blood parasites, at first called after their discoverer the "Leishman bodies," which have proved to be the effects of a _Piroplasma_.

_Trypanosoma_ is distinguished by the expansion of its flagellum into an undulating membrane, that runs down the edge of the body, and may project behind as a second lash. In this membrane run eight fine muscular filaments, or myonemes, four on either surface, within the undulating membrane; at their lower end they are all connected with a rounded body, the "blepharoplast," which is here in its origin, as well as in its behaviour in reproductive processes, a true modified nucleus, comparable in some respects, as was first noted by Plimmer and Rose Bradford,[133] with the micronucleus of the Infusoria. Part of the segmentation spindle persists in the form of a filament uniting the blepharoplast with the large true functional nucleus (Fig. 39, _a-f_).

The blood of patients suffering from relapsing fever contains a fine wriggling parasite, which was described as a Schizomycete, allied to the bacteria, and hitherto termed _Spirochaeta obermeieri_. Schaudinn has shown that this and other similar blood parasites are closely allied to _Trypanosoma_; and since the original genus was founded on organisms of putrefaction which are undoubtedly Schizomycetes, Vuillemin has suggested the name _Treponema_. _T. pallidum_ is found in syphilitic patients, and appears to be responsible for their illness.[134]

The Craspedomonadidae (often called Choanoflagellates, Fig. 40) are a group whose true nature was elucidated some forty years ago by the American zoologist, H. James-Clark. They are attached either to a substratum, by a stalk produced by the base of the cell, or to other members of the same colony; they are distinguished by the protrusion of the cytoplasm around the base of the single flagellum into a pellucid funnel,[135] in which the plasma is in constant motion, though the funnel retains its shape and size, except when, as sometimes happens, it is retracted.

{122}