Chapter XIII: Introduction: To Part III (2)

_Zoarium._ The zoarium is recumbent or erect, and is formed typically either of zooecia arising directly in cruciform formation from one another, or of zooecia joined together in similar formation with the intervention of tubules arising from their own bases. Complications often arise, however, either on account of the suppression of the lateral buds of a zooecium, so that the formation becomes linear instead of cruciform, or by the production in an irregular manner of additional tubules and buds from the upper part of the zooecia. A confused and tangled zoarium may thus be formed, the true nature of which can only be recognized by the examination of its terminal parts.

_Zooecia._ The zooecia are tubular and have a terminal or subterminal orifice, which is angulate or subangulate as seen from above. Owing to this fact, to the stiff nature of the external ectocyst, to the action of circular muscles that surround the tentacular sheath, and to the cylindrical form of the soft inverted part, the orifice, as seen from above, appears to form four flaps or valves, thus .

_Polypide._ The alimentary canal is elongate and slender as a whole, the oesophagus (including the pharynx) being of considerable length. In _Paludicella_ and _Pottsiella_ the oesophagus opens directly into the cardiac limb of the stomach, which is distinctly constricted at its base; but in _Victorella_ the base of the oesophagus is constricted off from the remainder to form an elongate oval sac the walls of which are lined with a delicate structureless membrane. _Victorella_ may therefore be said to possess a gizzard, but the structure that must be so designated has not the function (that of crushing food) commonly associated with the name, acting merely as a chamber for the retention of solid particles. In this genus the cardiac limb of the stomach is produced and vertical but not constricted at the base. The tentacles in most species number 8, but in _Paludicella_ there are 16.

_Resting buds._ The peculiar structures known in Europe as "hibernacula" are only found in this family. The name hibernacula, however, is inappropriate to the only known Indian species as they are formed in this country at the approach of summer instead of, as in Europe and N. America, at that of winter. It is best, therefore, to call them "resting buds." They consist of masses of cells congregated at the base of the zooecia, gorged with food material and covered with a resistant horny covering.

The family Paludicellidæ consists of three genera which may be distinguished as follows:--

I. Orifice terminal; main axis of the zooecium
vertical; zooecia separated from one another
by tubules.
[A. Base of the zooecia not swollen; no
adventitious buds POTTSIELLA.]
B. Base of the zooecium swollen; adventitious
buds produced near the tip VICTORELLA, p. 194.
II. Orifice subterminal, distinctly on the dorsal
surface; main axis of the zooecium horizontal
(the zoarium being viewed from the dorsal
surface); buds not produced at the tip of the
zooecia PALUDICELLA, p. 192.

Of these three genera, _Pottsiella_ has not yet been found in India and is only known to occur in N. America. It consists of one species, _P. erecta_ (Potts) from the neighbourhood of Philadelphia in the United States.

_Victorella_ includes four species, _V. pavida_ known from England and Germany and said to occur in Australia, _V. mülleri_ from Germany (distinguished by possessing parietal muscles at the tip of the zooecia), _V. symbiotica_ from African lakes and _V. bengalensis_ from India. These species are closely related.

_Paludicella_ is stated by Carter to have been found in Bombay, but probably what he really found was the young stage of _V. bengalensis_. A single species is known in Europe and N. America, namely _P. ehrenbergi_, van Beneden (=_Alcyonella articulata_, Ehrenberg).

I have examined specimens of all the species of this family as yet known.

Genus 1. PALUDICELLA, _Gervais_.

_Paludicella_, Gervais, Compt. Rend. iii, p. 797 (1836).

_Paludicella_, Allman, Mon. Fresh-Water Polyzoa, p. 113
(1857).

? _Paludicella_, Carter, Ann. Nat. Hist. (3) iii, p. 333
(1859).

_Paludicella_, Jullien, Bull. Soc. zool. France, x, p. 174
(1885).

_Paludicella_, Kraepelin, Deutsch. Süsswasserbryozoen, i, p.
96 (1887).

_Paludicella_, Loppens, Ann. Biol. lacustre, iv, p. 14
(1910).

_Zoarium._ The nature of the zoarium in this genus is well expressed by Ehrenberg's specific name "_articulata_," although the name was given under a false impression. The zooecia arise directly from one another in linear series with occasional side-branches. The side-branches are, however, often suppressed. The zoarium as a whole is either recumbent and adherent or at least partly vertical.

_Zooecia._ Although the zooecia are distinctly tubular as a whole, two longitudinal axes may be distinguished in each, for the tip is bent upwards in a slanting direction, bearing the orifice at its extremity. The main axis is, however, at right angles to the dorso-ventral axis, and the dorsal surface, owing to the position of the aperture, can always be readily distinguished from the ventral, even when the position of the zooecium is vertical. Each zooecium tapers towards the posterior extremity. Parietal muscles are always present.

A=a single zooecium with the polypide retracted. B=the base of the lophophore as seen from above with the tentacles removed. C=the orifice of a polypide with the collar expanded and the tentacles partly retracted. _a_=tentacles; _c_=collar; _d_=mouth; _e_=oesophagus; _f_=stomach; _g_=intestine; _k_=parieto-vaginal muscles; _p_=parietal muscles; _o_=cardiac part of the stomach; _r_=retractor muscle; _s_=funiculus.]

_Polypide._ The most striking features of the polypide are the absence of any trace of a gizzard and the highly specialized form assumed by the cardiac part of the stomach. There are two funiculi, both connecting the pyloric part of the stomach with the endocyst. The ovary develops at the end of the upper, the testis at that of the lower funiculus.

_Resting buds._ The resting buds are spindle-shaped.

Kraepelin recognized two species in the genus mainly by their method of growth and the number of tentacles. In his _P. mülleri_ the zoarium is always recumbent and the polypide has 8 tentacles, whereas in _P. articulata_ or _ehrenbergi_ the tentacles number 16 and upright branches are usually developed. It is probable, however, that the former species should be assigned to _Victorella_, for it is often difficult to distinguish _Paludicella_ from young specimens of _Victorella_ unless the latter bear adventitious terminal buds. The gizzard of _Victorella_ can be detected in well-preserved material even under a fairly low power of the microscope, and I have examined specimens of what I believe to be the adult of _mülleri_ which certainly belong to that genus.

It is always difficult to see the collar of _Paludicella_, because of its transparency and because of the fact that its pleats are apparently not strengthened by chitinous rods as is usually the case. Allman neither mentions it in his description of the genus nor shows it in his figures, and Loppens denies its existence, but it is figured by Kraepelin and can always be detected in well-preserved specimens, if they are examined carefully. If the collar were actually absent, its absence would separate _Paludicella_ not only from _Victorella_ and _Pottsiella_, but also from all other ctenostomes. In any case, _Victorella_ is distinguished from _Paludicella_ and _Pottsiella_ by anatomical peculiarities (_e. g._, the possession of a gizzard and the absence of a second funiculus) that may ultimately be considered sufficiently great to justify its recognition as the type and only genus of a separate family or subfamily.

The description of _Paludicella_ is included here on account of Carter's identification of the specimens he found at Bombay; but its occurrence in India is very doubtful.

Genus 2. _VICTORELLA_, _Kent_.

_Victorella_, Kent, Q. J. Micr. Sci. x, p. 34 (1870).

_Victorella_, Hincks, Brit. Marine Polyzoa, p. 559 (1880).

_Victorella_, Kraepelin, Deutsch. Süsswasserbryozoen, i, p.
93 (1887).

TYPE, _Victorella pavida_, Kent.

_Zoarium._ The zoarium consists primarily of a number of erect or semi-erect tubular zooecia joined together at the base in a cruciform manner by slender tubules, but complications are introduced by the fact that adventitious buds and tubules are produced, often in large numbers, round the terminal region of the zooecia, and that these buds are often separated from their parent zooecium by a tubule of considerable length, and take root among other zooecia at a distance from their point of origin. A tangled mass may thus be formed in which it is difficult to recognize the regular arrangement of the zooecia that can be readily detached at the growing points of the zoarium.

_Zooecia._ The zooecia when young closely resemble those of _Paludicella_, but as they grow the terminal upturned part increases rapidly, while the horizontal basal part remains almost stationary and finally appears as a mere swelling at the base of an almost vertical tube, in which by far the greater part, if not the whole, of the polypide is contained. Round the terminal part of this tube adventitious buds and tubules are arranged more or less regularly. There are no parietal muscles.

_Polypide._ The polypide has 8 slender tentacles, which are thickly covered with short hairs. The basal part of the oesophagus forms a thin-walled sac (the "gizzard") constricted off from the upper portion and bearing internally a thin structureless membrane. Circular muscles exist in its wall but are not strongly developed on its upper part. There is a single funiculus, which connects the posterior end of the stomach with the base of the zooecium. The ovaries and testes are borne on the endocyst, not in connection with the funiculus.

_Resting buds._ The resting buds are flattened or resemble young zooecia in external form.

_Victorella_, although found in fresh water, occurs more commonly in brackish water and is known to exist in the littoral zone of the sea.

26. Victorella bengalensis, _Annandale_.

_Victorella pavida_, Annandale (_nec_ Kent), Rec. Ind. Mus.
i, p. 200, figs. 1-4 (1907).

_Victorella bengalensis_, _id._, _ibid._ ii, p. 12, fig. 1
(1908).

_Zoarium._ _The mature zoarium resembles a thick fur_, the hairs of which are represented by elongate, erect, slender tubules (the zooecia), the arrangement of the whole being very complicated and irregular. The base of the zoarium often consists of an irregular membrane formed of matted tubules, which are sometimes agglutinated together by a gummy secretion. The zoarium as a whole has a faint yellowish tinge.

_Zooecia._ The zooecia when young are practically recumbent, each being of an ovoid form and having a stout, distinctly quadrate orificial tubule projecting upwards and slightly forwards near the anterior margin of the dorsal surface. At this stage a single tubule, often of great relative length, is often given off near the orifice, bearing a bud at its free extremity. As the zooecium grows the tubular part becomes much elongated as compared with the basal part and assumes a vertical position. Its quadrate form sometimes persists but more often disappears, so that it becomes almost circular in cross-section throughout its length. Buds are produced near the tip in considerable profusion. As a rule, if they appear at this stage, the tubule connecting them with the parent zooecium is short or obsolete; sometimes they are produced only on one side of the zooecium, sometimes on two. The buds themselves produce granddaughter and great-granddaughter buds, often connected together by short tubules, while still small and imperfectly developed. The swelling at the base of the zooecium, when the latter is fully formed, is small.

_Polypide._ The polypide has the features characteristic of the genus. The base of the gizzard is surrounded by a strong circular muscle.

A=single zooecium without adventitious buds but with a young resting bud (_b_), × 70 (dorsal view); B=lateral view of a smaller zooecium without buds, × 70; C=upper part of a zooecium with a single adventitious bud, × 70; D=outline of the upper part of a zooecium with adventitious buds of several generations, × 35; E=remains of a zooecium with two resting buds (_b_) attached. All the specimens figured are from Port Canning and, except D, are represented as they appear when stained with borax carmine and mounted in canada balsam.]

_Resting buds._ The resting buds (fig. 31, p. 170) are somewhat variable in shape but are always flat with irregular cylindrical or subcylindrical projections round the margin, on which the horny coat is thinner than it is on the upper surface. This surface is either smooth or longitudinally ridged.

TYPE in the Indian Museum.

This species differs from the European _V. pavida_ in very much the same way as, but to a greater extent than, the Indian race of _Bowerbankia caudata_ does from the typical English one (see p. 189). The growth of the zoarium is much more luxuriant, and the form of the resting buds is different.

GEOGRAPHICAL DISTRIBUTION.--_V. bengalensis_ is abundant in pools of brackish water in the Ganges delta and in the Salt Lakes near Calcutta; it also occurs in ponds of fresh water near the latter. I have received specimens from Madras from Dr. J. R. Henderson, and it is probable that the form from Bombay referred by Carter to _Paludicella_ belonged to this species.

BIOLOGY.--In the Ganges delta _V. bengalensis_ is usually found coating the roots and stems of a species of grass that grows in and near brackish water, and on sticks that have fallen into the water. It also spreads over the surface of bricks, and I have found a specimen on a living shell of the common mollusc _Melania tuberculata_. Dr. Henderson obtained specimens at Madras from the surface of a freshwater shrimp, _Palæmon malcolmsonii_. In the ponds at Port Canning the zoaria grow side by side with, and even entangled with those of _Bowerbankia caudata_ subsp. _bengalensis_, to the zooecia of which their zooecia bear a very strong external resemblance so far as their distal extremity is concerned. This resemblance, however, disappears in the case of zooecia that bear terminal buds, for no such buds are borne by _B. caudata_; and the yellowish tint of the zoaria of _V. bengalensis_ is characteristic. Zoaria of the entoproct _Loxosomatoides colonialis_ and colonies of the hydroid _Irene ceylonensis_ are also found entangled with the zoaria of _V. bengalensis_, the zooecia of which are often covered with various species of Vorticellid protozoa and small rotifers. The growth of _V. bengalensis_ is more vigorous than that of the other polyzoa found with it, and patches of _B. caudata_ are frequently surrounded by large areas of _V. bengalensis_.

The food of _V. bengalensis_ consists largely of diatoms, the siliceous shells of which often form the greater part of its excreta. Minute particles of silt are sometimes retained in the gizzard, being apparently swallowed by accident.

There are still many points to be elucidated as regards the production and development of the resting buds in _V. bengalensis_, but two facts are now quite clear as regards them: firstly, that these buds are produced at the approach of the hot weather and germinate in November or December; and secondly, that the whole zoarium may be transformed at the former season into a layer of resting buds closely pressed together but sometimes exhibiting in their arrangement the typical cruciform formation. Resting buds may often be found in vigorous colonies as late as the beginning of December; these buds have not been recently formed but have persisted since the previous spring and have not yet germinated. Sometimes only one or two buds are formed at the base of an existing zooecium (fig. 37 _a_), but apparently it is possible not only for a zooecium to be transformed into a resting bud but for it to produce four other buds round its base before undergoing the change. Young polypides are formed inside the buds and a single zooecium sprouts out of each, as a rule by the growth of one of the basal projections, when conditions are favourable.

Polypides of _V. bengalensis_ are often transformed into brown bodies. When this occurs the orifice closes together, with the collar expanded outside the zooecium. I have occasionally noticed that the ectocyst of such zooecia was distinctly thicker and darker in colour than that of normal zooecia.

Eggs and spermatozoa are produced in great numbers, as a rule simultaneously in the same zooecia, but individuals kept in captivity often produce spermatozoa only. The eggs are small and are set free as eggs. Nothing is known as regards their development.

Polypides are as a rule found in an active condition only in the cold weather, but I have on one occasion seen them in this condition in August, in a small zoarium attached to a shell of _Melania tuberculata_ taken in a canal of brackish water near Calcutta.

Family HISLOPIIDÆ.

HISLOPIDÉES, Jullien, Bull. Soc. zool. France, x, p. 180
(1885).

HISLOPIIDÆ, Annandale, Rec. Ind. Mus. i, p. 200 (1907).

_Zoarium_ recumbent, often forming an almost uniform layer on solid subjects.

_Zooecia_ flattened, adherent; the orifice dorsal, either surrounded by a chitinous rim or situated at the tip of an erect chitinous tubule; no parietal muscles.

_Polypide_ with an ample gizzard which possesses a uniform chitinous lining and does not close together when the polypide is retracted.

_Resting bud_, not produced.

Only two genera can be recognized in this family, _Arachnoidea_, Moore, from Central Africa, and _Hislopia_, Carter, which is widely distributed in Eastern Asia. The former genus possesses an upright orificial tubule and has zooecia separated by basal tubules. Its anatomy is imperfectly known, but it certainly possesses a gizzard of similar structure to that of _Hislopia_, between which and _Victorella_ its zooecium is intermediate in form.

Genus HISLOPIA, _Carter_.

_Hislopia_, Carter, Ann. Nat. Hist. (3) i, p. 169 (1858).

_Hislopia_, Stolickza, J. As. Soc. Bengal, xxxviii (2), p.
61 (1869).

_Norodonia_, Jullien, Bull. Soc. zool. France, v, p. 77
(1880).

_Hislopia_, _id._, _ibid._ x, p. 183 (1885).

_Norodonia_, _id._, _ibid._ p. 180.

_Echinella_, Korotneff, Biol. Centrbl. xxi, p. 311 (1901).

_Hislopia_, Annandale, J. As. Soc. Bengal (new series) ii,
p. 59 (1906).

_Hislopia_, Loppens, Ann. Biol. lacustre, iii, p. 175
(1908).

TYPE, _Hislopia lacustris_, Carter.

_Zoarium._ The zoarium consists primarily of a main axis running in a straight line, with lateral branches that point forwards and outwards. Further proliferation, however, often compacts the structure into an almost uniform flat area.

_Zooecia._ The zooecia (fig. 35 B, p. 190) are flat and have the orifice surrounded by a chitinous rim but not much raised above the dorsal surface. They arise directly one from another.

_Polypide._ The polypide possesses from 12 to 20 tentacles. Its funiculus is rudimentary or absent. Neither the ovaries nor the testes have any fixed position on the lateral walls of the zooecium to which they are confined.

The position of this genus has been misunderstood by several zoologists. Carter originally described _Hislopia_ as a cheilostome allied to _Flustra_; in 1880 Jullien perpetuated the error in describing his _Norodonia_, which was founded on dried specimens of Carter's genus; while Loppens in 1908 still regarded the two "genera" as distinct and placed them both among the cheilostomes. In 1885, however, Jullien retracted his statement that _Norodonia_ was a cheilostome and placed it, together with _Hislopia_, in a family of which he recognized the latter as the eponymic genus. Carter's mistake arose from the fact that he had only examined preserved specimens, in which the thickened rim of the orifice is strongly reminiscent of the "peristome" of certain cheilostomes, while the posterior of the four folds into which the tentacle sheath naturally falls (as in all ctenostomes, _cf._ the diagram on p. 191) is in certain conditions rather larger than the other three and suggests the "lip" characteristic of the cheilostomes. If living specimens are examined, however, it is seen at once that the posterior fold, like the two lateral folds and the anterior one, changes its form and size from time to time and has no real resemblance to a "lip."

That there is a remarkable, if superficial, resemblance both as regards the form of the zooecium and as regards the method of growth between _Hislopia_ and certain cheilostomes cannot be denied, but the structure of the orifice and indeed of the whole organism is that of a ctenostome and the resemblance must be regarded as an instance of convergence rather than of genetic relationship.

The most striking feature of the polypide of _Hislopia_ is its gizzard (fig. 38, p. 201) which is perhaps unique (except for that of _Arachnoidea_) both in structure and function. In structure its peculiarities reside mainly in three particulars: (i), it is not constricted off directly from the thin-walled oesophageal tube, but possesses at its upper extremity a thick-walled tubular portion which can be entirely closed from the oesophagus at its upper end but always remains in communication with the spherical part of the gizzard; (ii), this spherical part of the gizzard is uniformly lined with a thick chitinous or horny layer which in optical section has the appearance of a pair of ridges; and (iii), there is a ring of long and very powerful cilia round the passage from the gizzard to the stomach. The cardiac limb of the stomach, which is large and heart-shaped, is obsolete. The wall of the spherical part of the gizzard consists of two layers of cells, an outer muscular layer consisting of powerful circular muscles and an inner glandular layer, which secretes the chitinous lining. The inner walls of the tubular part consist of non-ciliated columnar cells, and when the polypide is retracted it lies almost at right angles to the main axis of the zooecium.

The spherical part of the gizzard invariably contains a number of green cells, which lie free in the liquid it holds and are kept in motion by the cilia at its lower aperture. The majority of these cells can be seen with the aid of a high power of the microscope to consist of a hard spherical coat or cyst containing green protoplasm in which a spherical mass of denser substance (the nucleus) and a number of minute transparent granules can sometimes be detected. The external surface of many of the cysts is covered with similar granules, but some are quite clean.

There can be no doubt that these cysts represent a stage in the life-history of some minute unicellular plant or animal. Indeed, although it has not yet been found possible to work out this life-history in detail, I have been able to obtain much evidence that they are the resting stage of a flagellate organism allied to _Euglena_ which is swallowed by the polyzoon and becomes encysted in its gizzard, extruding in so doing from its external surface a large proportion of the food-material that it has stored up within itself in the form of transparent granules. It may also be stated that some of the organisms die and disintegrate on being received into the gizzard, instead of encysting themselves.

So long as the gizzard retains its spherical form the green cells and its other contents are prevented from entering the stomach by the movements of the cilia that surround its lower aperture, but every now and then, at irregular intervals, the muscles that form its outer wall contract. The chitinous lining although resilient and not inflexible is too stiff to prevent the lumen of the gizzard being obliterated, but the action of the muscles changes its contents from a spherical to an ovoid form and in so doing presses a considerable part of them down into the stomach, through the ring of the cilia.

The contraction of the gizzard is momentary, and on its re-expansion some of the green cysts that have entered the stomach are often regurgitated into it. Some, however, remain in the stomach, in which they are turned round and round by the action of the cilia at both apertures. They are apparently able to retain their form for some hours in these circumstances but finally disintegrate and disappear, being doubtless digested by the juices poured out upon them by the glandular lining of the stomach. In polypides kept under observation in clean tap-water all the cysts finally disappear, and the fæces assume a green colour. In preserved specimens apparently unaltered cysts are sometimes found in the rectum, but this is exceptional: I have observed nothing of the kind in living polypides. Cysts often remain for several days unaltered in the gizzard.

Imperfect as these observations are, they throw considerable light on the functions of the gizzard in _Hislopia_. Primarily it appears to act as a food-reservoir in which the green cysts and other minute organisms can be kept until they are required for digestion. When in the gizzard certain organisms surrender a large proportion of the food-material stored up for their own uses, and this food-material doubtless aids in nourishing the polyzoon. Although the cysts in the gizzard are frequently accompanied by diatoms, the latter are not invariably present. The cysts, moreover, are to be found in the zooecia of polypides that have formed brown bodies, often being actually enclosed in the substance of the brown body. The gizzards of the specimens of _Arachnoidea_ I have examined contain cysts that resemble those found in the same position in _Hislopia_.

_Hislopia_ is widely distributed in the southern part of the Oriental Region, and, if I am right in regarding _Echinella_, Korotneff as a synonym, extends its range northwards to Lake Baikal. It appears to be a highly specialized form but is perhaps related, through _Arachnoidea_, to _Victorella_.

27. Hislopia lacustris, _Carter_.

_Hislopia lacustris_, Carter, Ann. Nat. Hist. (3) i, p. 170,
pl. vii, figs. 1-3 (1858).

_Norodonia cambodgiensis_, Jullien, Bull. Soc. zool. France,
v, p. 77, figs. 1-3 (1880).

_Norodonia sinensis_, _id._, _ibid._ p. 78, figs. 1-3.

_Norodonia cambodgiensis_, _id._, _ibid._ x, p. 181, figs.
244, 245 (1885).

_Norodonia sinensis_, _id._, _ibid._ p. 182, figs. 246, 247.

_Hislopia lacustris_, Annandale, J. As. Soc. Bengal (new
series) iii, p. 85 (1907).

_Hislopia lacustris_, Walton, Rec. Ind. Mus. i, p. 177
(1907).

_Hislopia lacustris_, Kirkpatrick, _ibid._ ii, p. 98 (1908).

_Hislopia lacustris_, Walton, _ibid._ iii, p. 295 (1909).

_Zoarium._ The zoarium forms a flat, more or less solid layer and is closely adherent to foreign objects. As a rule it covers a considerable area, with radiating branches at the edges; but when growing on slender twigs or the stems of water-plants it forms narrow, closely compressed masses. One zooecium, however, never grows over another.

_Zooecia._ The zooecia are variable in shape. In zoaria which have space for free expansion they are as a rule irregularly oval, the posterior extremity being often narrower than the anterior; but small triangular zooecia and others that are almost square may often be found. When growing on a support of limited area the zooecia are smaller and as a rule more elongate. The orifice is situated on a slight eminence nearer the anterior than the posterior margin of the dorsal surface. It is surrounded by a strong chitinous rim, which is usually square or subquadrate but not infrequently circular or subcircular. Sometimes a prominent spine is borne at each corner of the rim, but these spines are often vestigial or absent; they are rarely as long as the transverse diameter of the orifice. The zooecium is usually surrounded by a chitinous margin, and outside this margin there is often a greater or less extent of adherent membrane. In some zooecia the margin is obsolete or obsolescent. The dorsal surface is of a glassy transparency but by no means soft.

A=part of a zoarium of the subspecies _moniliformis_ (type specimen, from Calcutta), × 15; A=green cysts in gizzard; E=eggs.

B=outline of part of a zoarium of the typical form of the species from the United Provinces, showing variation in the form of the zooecia and of the orifice, × 15.]

_Polypide._ The polypide has from 12 to 20 tentacles, 16 being a common number.

TYPE probably not in existence. It is not in the British Museum and Prof. Dendy, who has been kind enough to examine the specimens from Carter's collection now in his possession, tells me that there are none of _Hislopia_ among them.

27 _a._ Subsp. moniliformis, nov.

_Hislopia lacustris_, Annandale, J. As. Soc. Bengal (new
series) ii, p. 59, fig. 1 (1906).

In this race, which is common in Calcutta, the zooecia are almost circular but truncate or concave anteriorly and posteriorly. They form linear series with few lateral branches. I have found specimens occasionally on the shell of _Vivipara bengalensis_, but they are much more common on the leaves of _Vallisneria spiralis_.

TYPE in the Indian Museum.

The exact status of the forms described by Jullien as _Norodonia cambodgiensis_ and _N. sinensis_ is doubtful, but I see no reason to regard them as specifically distinct from _H. lacustris_, Carter, of which they may be provisionally regarded as varieties. The variety _cambodgiensis_ is very like my subspecies _moniliformis_ but has the zooecia constricted posteriorly, while var. _sinensis_, although the types were found on _Anodonta_ shells on which there was plenty of room for growth, resemble the confined phase of _H. lacustris_ so far as the form of their zooecia and of the orifice is concerned.

GEOGRAPHICAL DISTRIBUTION.--The typical form is common in northern India and occurs also in Lower Burma; the subspecies _moniliformis_ appears to be confined to Lower Bengal, while the varieties _cambodgiensis_ and _sinensis_ both occur in China, the former having been found also in Cambodia and Siam. Indian and Burmese localities are:--BENGAL, Calcutta (subsp. _moniliformis_); Berhampur, Murshidabad district (_J. Robertson Milne_): CENTRAL PROVINCES, Nagpur (_Carter_): UNITED PROVINCES, Bulandshahr (_H. J. Walton_): BURMA, Pegu-Sittang Canal (_Kirkpatrick_).

BIOLOGY.--Regarding the typical form of the species Major Walton writes (Rec. Ind. Mus. iii, p. 296):--"In volume i (page 177) of the Records of the Indian Museum, I described the two forms of colonies of _Hislopia_ that I had found in the United Provinces (Bulandshahr). Of these, one was a more or less linear arrangement of the zooecia on leaves and twigs, and the other, and more common, form was an encrusting sheath on the outer surface of the shells of _Paludina_. During the present 'rains' (July 1908) I have found many examples of what may be considered a much exaggerated extension of the latter form. These colonies have been on bricks, tiles, and other submerged objects. The largest colony that I have seen so far was on a tile; one side of the tile was exposed above the mud of the bottom of the tank, and its area measured about 120 square inches; the entire surface was almost completely covered by a continuous growth of _Hislopia_. Another large colony was on a piece of bark which measured 7 inches by 3 inches; both sides were practically everywhere covered by _Hislopia_."

Major Walton also notes that in the United Provinces the growth of _Hislopia_ is at its maximum during "rains," and that at that time of year almost every adult _Paludina_ in a certain tank at Bulandshahr had its shell covered with the zooecia. The Calcutta race flourishes all the year round but never forms large or closely compacted zoaria, those on shells of _Vivipara_ exactly resembling those on leaves of _Vallisneria_.

In Calcutta both eggs and spermatozoa are produced at all times of the year simultaneously in the same zooecia, but the eggs in one zooecium often vary greatly in size. When mature they reach relatively considerable dimensions and contain a large amount of food material; but they are set free from the zooecium as eggs. They lie loose in the zooecium at a comparatively small size and grow in this position. Nothing is known as regards the development of _Hislopia_.

Both forms of the species appear to be confined to water that is free from all traces of contamination with brine.

Order PHYLACTOLÆMATA.

The polypide in this order possesses a leaf-like ciliated organ (the epistome) which arises within the lophophore between the mouth and the anus and projects upwards and forwards over the mouth, which it can be used to close. The zooecia are never distinct from one another, but in dendritic forms such as _Plumatella_ the zoarium is divided at irregular intervals by chitinous partitions. The lophophore in most genera is horseshoe-shaped instead of circular, the part opposite the anus being deeply indented. There are no parietal muscles. The orifice of the zooecium is always circular, and there is no trace of any structure corresponding to the collar of the ctenostomes. The tentacles are always webbed at the base.

All the phylactolæmata produce the peculiar reproductive bodies known as statoblasts.

The phylactolæmata, which are probably descended from ctenostomatous ancestors, are confined to fresh or slightly brackish water. Most of the genera have a wide geographical distribution, but (with the exception of a few statoblasts of almost recent date) only one fossil form (_Plumatellites_, Fric. from the chalk of Bohemia) has been referred to the order, and that with some doubt.

It is convenient to recognize two main divisions of the phylactolæmata, but these divisions hardly merit the distinction of being regarded as suborders. They may be called Cristatellina and Plumatellina and distinguished as follows:--

Division I, PLUMATELLINA, nov.--Ectocyst well developed; zoaria without a special organ of progression; polypides contained in tubes.

Division II, CRISTATELLINA, nov.--Ectocyst absent except at the base of the zoarium which is modified to form a creeping "sole"; polypides embedded in a common synoecium of reticulate structure.

The Cristatellina consist of a single genus and probably of a single species (_Cristatella mucedo_, Cuvier), which is widely distributed in Europe and N. America, but has not been found in the Oriental Region. Eight genera of Plumatellina are known, and five (possibly six) of these genera occur in India.

Division PLUMATELLINA, nov.

The structure of the species included in this division is very uniform as regards the internal organs (see fig. 40 opposite and fig. 47 _a_, p. 236). The alimentary canal is simpler than that of the Paludicellidæ. A short oesophagus leads directly into the stomach, the cardiac portion of which is produced as a vertical limb almost cylindrical in form and not constricted at the base. This limb is as a rule of greater length than the oesophagus. The pyloric part of the stomach is elongated and narrow, and the intestine short, straight, and of ovoid form. There are no cilia at the pyloric opening. A single funiculus joins the posterior end of the stomach to the wall of the zooecium, bearing the statoblasts. Sexual organs are often absent.

A=a zooecium of _Fredericella_ with the polypide extruded. B=the lophophore of _Lophopus_ (tentacles removed) as seen obliquely from the right side. C=larva of _Plumatella_ as seen in optical section. _a_=tentacles; _b_=velum; _c_=epistome; _d_=mouth; _e_=oesophagus; _f_=stomach; _g_=intestine; _h_=anus; _j_=retractor muscle; _k_=parieto-vaginal muscles; _l_=funiculus.]

Two families may be recognized as constituting the division, _viz._, (_a_) the Fredericellidæ, which have a circular or oval lophophore and simple statoblast without a swim-ring, and (_b_) the Plumatellidæ, in which the lophophore is shaped like a horseshoe and some or all of the statoblasts are provided with a ring of air-spaces.

Family 1. FREDERICELLIDÆ.

FREDERICELLIDÆ, Kraepelin, Deutsch. Süsswasserbryozoen, i,
p. 168 (1887).

_Zoaria_ dendritic; _zooecia_ distinctly tubular, with the ectocyst well developed; _statoblasts_ of one kind only, each surrounded by a chitinous ring devoid of air-spaces; _polypides_ with the lophophore circular or oval when expanded.

The Fredericellidæ consist of a single genus (_Fredericella_) which includes several closely-allied forms and has a wide geographical distribution.

Genus FREDERICELLA, _Gervais_ (1838).

_Fredericella_, Allman, Mon. Fresh-Water Polyzoa, p. 11
(1857).

_Plumatella_, ("arrêt de développement") Jullien, Bull. Soc.
zool. France, x, p. 121 (1885).

_Fredericella_, Kraepelin, Deutsch. Süsswasserbryozoen,
i, p. 99 (1887).

_Fredericella_, Goddard, Proc. Linn. Soc. N. S. Wales,
xxxiv, p. 489 (1909).

This genus has the characters of the family. Its status has been much disputed, some authors regarding the shape of the lophophore as of great morphological importance, while Jullien believed that _Fredericella_ was merely an abnormal or monstrous form of _Plumatella_. The latter belief was doubtless due to the fact that the zoaria of the two genera bear a very close external resemblance to one another and are sometimes found entangled together. The importance of the shape of the lophophore may, however, easily be exaggerated, for, as both Jullien and Goddard have pointed out, it assumes an emarginate form when retracted.

The best known species is the European and N. American _F. sultana_ (Blumenbach), of which several varieties or phases have been described as distinct. This form is stated to occur also in S. Africa. _F. australiensis_, Goddard[BC] from N. S. Wales is said to differ from this species in having an oval instead of a circular lophophore and in other small anatomical characters; but it is doubtful how far these characters are valid, for the lophophore appears to be capable of changing its shape to some slight extent and has been stated by Jullien to be habitually oval in specimens from France. _F. cunningtoni_, Rousselet[BD] from Lake Tanganyika has stout zooecia encrusted with relatively large sand-grains.

[Footnote BC: Proc. Linn. Soc. N. S. Wales, xxxiv, p. 489
(1909).]

[Footnote BD: Rousselet, Proc. Zool. Soc. London, 1907 (1),
p. 254.]

The zoaria of _Fredericella_ are usually found attached to solid objects in shallow water, but a form described as _F. duplessisi_, Ford has been found at a depth of 40 fathoms embedded in mud at the bottom of the Lake of Geneva. _F. cunningtoni_ was dredged from depths of about 10 and about 25 fathoms.

The statoblasts of this genus do not float and often germinate in the parent zooecium after its polypides have died. They are produced in smaller numbers than is usually the case in other genera of the order. The polypides sometimes undergo a process of regeneration, but without the formation of brown bodies.

A=statoblast, × 120. B=outline of expanded lophophore and adjacent parts, × 75; a=anus, r=rectum. C=outline of zoarium on leaf of water-plant, × 3.

(A and B are from specimens from Igatpuri, C from specimen from Shasthancottah).]

28. Fredericella indica, _Annandale_.

_Fredericella indica_, Annandale, Rec. Ind. Mus. iii, p. 373,
fig. (1909).

_Fredericella indica_, _id._, _ibid._ v, p. 39 (1910).

_Zoarium._ The zoarium is of delicate appearance and branches sparingly. It is often entirely recumbent but sometimes produces short, lax branches that consist of two or three zooecia only.

_Zooecia._ The zooecia are very slender and almost cylindrical; they are slightly emarginate and furrowed, the keel in which the furrow runs being sometimes prominent. The external surface is minutely roughened and apparently soft, for small grains of sand and other débris cling to it, but never thickly. The ectocyst is practically colourless but not transparent.

_Statoblasts._ The statoblasts are variable in size and form but most commonly have a regular broad oval outline; sometimes they are kidney-shaped. The dorsal surface is covered with minute star-shaped prominences, which sometimes cover it almost uniformly and are sometimes more numerous in the centre than towards the periphery. The ventral surface is smooth.

_Polypide._ The lophophore bears about 20-25 tentacles, which are very slender and of moderate length; the velum at their base is narrow; as a rule the lophophore is accurately circular.

TYPE in the Indian Museum.

The most definite character in which this species differs from _F. sultana_ and _F. australiensis_ is the ornamentation of one surface of the statoblast, both surfaces of which are smooth in the two latter species. From _F. cunningtoni_, the statoblasts of which are unknown, it differs in having almost cylindrical instead of depressed zooecia and in not having the zooecia densely covered with sand-grains.

GEOGRAPHICAL DISTRIBUTION.--Western India (the Malabar Zone): Igatpuri Lake, W. Ghats (alt. ca. 2,000 feet), Bombay Presidency, and Shasthancottah Lake near Quilon, Travancore.

BIOLOGY.--In both the lakes in which the species has yet been found it was collected in November. The specimens obtained in Travancore were found to be undergoing a process of regeneration due at least partly to the fact that most of the polypides had perished and that statoblasts were germinating in the old zooecia. Specimens from the Bombay Presidency, which were obtained a little later in the month, were in a more vigorous condition, although even they contained many young polypides that were not yet fully formed. It seems, therefore, not improbable that _F. indica_ dies down at the beginning of the hot weather and is regenerated by the germination of its statoblasts at the beginning of the cold weather.

At Shasthancottah zoaria were found entangled with zoaria of a delicate form of _Plumatella fruticosa_ to which they bore a very close external resemblance.

Family 2. PLUMATELLIDÆ.

PLUMATELLIDÆ, Allman (_partim_), Mon. Fresh-Water Polyzoa,
pp. 76, 81 (1857).

Phylactolæmata which have horseshoe-shaped lophophores and a well-developed ectocyst not specialized to form an organ of progression. Some or all of the statoblasts are provided with a "swim-ring" consisting of symmetrically disposed, polygonal chitinous chambers containing air.

It is convenient to divide the Plumatellidæ as thus defined into subfamilies (the Plumatellinæ and the Lophopinæ), which may be defined as follows:--

Subfamily A. PLUMATELLINÆ.

Zoarium dendritic or linear, firmly fixed to extraneous objects; zooecia tubular, not fused together to form a gelatinous mass.

Subfamily B. LOPHOPINÆ.

Zoarium forming a gelatinous mass in which the tubular nature of the zooecia almost disappears, capable to a limited extent of progression along a smooth surface.

Both these subfamilies are represented in the Indian fauna, the Plumatellinæ by two of the three genera known to exist, and the Lophopinæ by two (or possibly three) of the four that have been described. The following key includes all the known genera, but the names of those that have not been recorded from India are enclosed in square brackets.

_Key to the Genera of_ Plumatellidæ.

I. Statoblasts without marginal processes.
A. Zooecia cylindrical, not embedded in a gelatinous
investment (Plumatellinæ).
_a_. Zooecia arising directly from one another;
no stolon; free statoblast oval PLUMATELLA, p. 212.
_a'_. Zooecia arising singly or in groups from
an adherent stolon; free statoblasts oval. STOLELLA, p. 229.
B. Zooecia cylindrical, embedded in a structureless
gelatinous investment.
Zooecia arising from a ramifying stolon;
statoblasts circular [STEPHANELLA.]
C. Polypides embedded in a hyaline synoecium
that conceals the cylindrical form of the
zooecia (Lophopinæ).
_c_. Polypides upright, their base far removed
from that of the zoarium when they are
expanded LOPHOPUS, p. 231.
_c'_. Polypides recumbent for the greater
part of their length at the base of
the zoarium [AUSTRALELLA[BE].]
II. Statoblasts armed (normally) with hooked
processes (Lophopinæ).
A. Processes confined to the extremities of
the statoblast; zoaria remaining separate
throughout life LOPHOPODELLA, p. 231.
B. Processes entirely surrounding the
statoblast; many zoaria embedded in a
common gelatinous investment so as to
form large compound colonies PECTINATELLA, p. 235.

[Footnote BE: See Rec. Ind. Mus. v, p. 40, footnote (1910).]

Subfamily A. PLUMATELLINÆ.

Of the two Indian genera of this subfamily, one (_Plumatella_) is almost universally distributed, while the other (_Stolella_) has only been found in the valley of the Ganges. The third genus of the subfamily (_Stephanella_) is only known from Japan.

It should be noted that zoaria of different species and genera of this subfamily are often found in close proximity to one another and to zoaria of _Fredericella_, and that the branches of the different species are sometimes entangled together in such a way that they appear, unless carefully separated, to belong to the same zoarium.

Genus 1. PLUMATELLA, _Lamarck_.

_Plumatella_, Lamarck, Animaux sans Vert. (ed. 1re) ii, p.
106 (1816).

_Alcyonella_, _id_., _ibid_. p. 100.

_Plumatella_, Allman, Mon. Fresh-Water Polyzoa, p. 92
(1857).

_Alcyonella_, _id_., _ibid_. p. 86.

_Plumatella_, Hyatt, Comm. Essex Inst. iv, p. 207, pl. viii
(1866).

_Plumatella_, Jullien (_partim_), Bull. Soc. zool. France,
x, p. 100 (1885).

_Hyalinella_, _id_., _ibid_. p. 133.

_Plumatella_, Kraepelin, Deutsch. Süsswass. Bryozoen, i, p.
104 (1887).

_Plumatella_, Braem, Unter. ü. Bryozoen des süssen Wassers,
p. 2 (Bibliotheca Zoologica, ii, 1890).

_Zoarium_ dendritic, recumbent, erect, or partly recumbent and partly erect.

_Zooecia_ tubular, not confined in a gelatinous synoecium; the ectocyst usually horny.

_Statoblasts_ often of two kinds, free and stationary, the latter without air-cells and as a rule adherent by one surface, the former provided with a well-developed ring of air-cells but without marginal processes, oval in form, never more than about 0.6 mm. in length.

_Polypide_ with less than 65 tentacles.

A, of _P. fruticosa_ (Calcutta); B, of _P. emarginata_ (Calcutta); C, of _P. javanica_ (Travancore); D, of _P. diffusa_ (Sikhim); E, of _P. allmani_ (Bhim Tal); F, of _P. diffusa_ (Rajshahi, Bengal); G, G', of _P. punctata_ (Calcutta); H, of _P. diffusa_ (Sikhim), statoblast further enlarged: A=outline of capsule; B=limit of swim-ring on ventral surface; C=limit of swim-ring on dorsal surface. [The dark area represents the capsule of the statoblast.]]

Certain forms of this genus are liable to become compacted together in such a way as to constitute solid masses consisting of elongate vertical zooecia closely parallel to one another and sometimes agglutinated by means of a gummy substance. These forms were given by Lamarck in 1816 the name _Alcyonella_, and there has been much dispute as to whether they represent a distinct genus, distinct species, or merely varieties or phases of more typical forms. It appears to be the case that all species which produce vertical branches are liable to have these branches closely packed together and the individual zooecia of which they are composed more or less greatly elongated. It is in this way that the form known to Allman as _Alcyonella benedeni_ is produced from the typical _Plumatella emarginata_. Other forms go further and secrete a gummy substance that glues the upright zooecia together and forces them to elongate themselves without branching. In these conditions the zooecia become polygonal in cross-section. It is probable that such forms (_e. g._, _Plumatella fungosa_ (Pallas)) should rank as distinct species, for the gummy secretion is present in great profusion even in young zoaria in which the zooecia have not yet assumed a vertical position. No such form, however, has as yet been found in India, and in any case it is impossible to regard _Alcyonella_ as a distinct genus.

_Key to the Indian Species of_ Plumatella.

I. Ectocyst more or less stiff, capable of
transverse wrinkling only near the tips of
the zooecia, never contractile or greatly
swollen; zooecia rounded[BF] at the tip when
the polypide is retracted. Free statoblasts
elongate; the free portion of their swim-ring
distinctly narrower at the sides than at
the ends.
A. Ectocyst by no means rigid, of a uniform
pale colour; zooecia never emarginate or
furrowed, straight, curved or sinuous,
elongate, cylindrical _fruticosa_, p. 217.
B. Ectocyst rigid; zooecia (or at any rate
some of the zooecia) emarginate and furrowed.
_b_. Ectocyst darkly pigmented over the
greater part of each zooecium, white
at the tip; branching of the zoarium
practically dichotomous, profuse, as
a rule both horizontal and vertical;
zooecia straight or slightly curved
or sinuous _emarginata_, p. 220.
_b'_. Ectocyst colourless and hyaline;
branching of the zoarium sparse,
lateral, irregular, horizontal;
zooecia nearly straight, strongly
emarginate and furrowed _javanica_, p. 221.
_b''_. The majority of the zooecia distinctly
L-shaped, one limb being as a rule
adherent; ectocyst never densely
pigmented.
beta. Zooecia cylindrical, their furrowed
keel never prominent _diffusa_, p. 223.
beta'. Zooecia (or at any rate some of the
zooecia) constricted or tapering at
the base, their emargination and
furrow conspicuous _allmani_, p. 224.

II. Ectocyst stiff; zooecia truncated when the
polypide is retracted. Surface of zooecia
minutely roughened, distinctly annulate on
the distal part _tanganyikæ_, p. 225.
III. Ectocyst swollen and contractile, capable
of transverse wrinkling all over the
zooecium; zooecia never emarginate _punctata_, p. 227.

[Footnote BF: In specimens preserved in spirit they are apt
to collapse and therefore to become somewhat concave.]

There has always been much difficulty in separating the species of _Plumatella_, and even now there is no general consensus of opinion as to the number that should be recognized. The difficulty, however, is much reduced if the following precautions are observed:--

(1) If the zoarium appears to be tangled, if the branches
intertwine or overlap, or if the zooecia are closely pressed
together, the whole mass should be carefully dissected out.
This is necessary not only because zoaria belonging to
different species are sometimes found entangled together but
also because it is often difficult to recognize the
characteristic method of branching and shape of the zooecia
unless it is done.

(2) As large a part as possible of each zoarium should be
examined, preferably with a binocular microscope, and
allowance should be made for irregularities and
abnormalities of all kinds. What must be observed is the
rule rather than the exceptions.

(3) When the statoblasts are being examined, care must be
taken that they lie flat and that their surface is parallel
to that of the nose-piece of the microscope. If they are
viewed obliquely it is impossible to see their true outlines
and proportions.

(4) In order to see the relative proportions of the capsule
and the swim-ring it is necessary that the statoblast should
be rendered transparent. This is often difficult owing to
the presence of air in the air-cells, but strong nitric acid
applied judiciously will render it possible (p. 240).

In supervising the preparation of the plates that illustrate this genus I have impressed upon the artist the importance of representing what he saw rather than what he thought he ought to see, and the figures are very close copies of actual specimens. I have deliberately chosen for representation specimens of _Plumatella_ preserved by the simple methods which are often the only ones that it is possible for a traveller to adopt, for the great majority of naturalists will probably have no opportunity of examining living specimens or specimens preserved by special methods, and the main object, I take it, of this series is to enable naturalists first to distinguish the species described and then to learn something of their habitat and habits.

GEOGRAPHICAL DISTRIBUTION.--Of the seven species included in this key five have been found in Europe (namely _P. fruticosa_, _P. emarginata_, _P. diffusa_, _P. allmani_, and _P. punctata_), while of these five all but _P. allmani_ are known to occur in N. America also. _P. javanica_ is apparently peculiar to the Oriental Region, while _P. tanganyikæ_ has only been taken in Central Africa and in the Bombay Presidency.

TYPES.--Very few of the type-specimens of the older species of _Plumatella_ are in existence. Allman's are neither in Edinburgh nor in London, and Mr. E. Leonard Gill, who has been kind enough to go through the Hancock Collection at Newcastle-on-Tyne, tells me that he cannot trace Hancock's. Those of the forms described by Kraepelin are in Hamburg and that of _P. tanganyikæ_ in the British Museum, and there are schizotypes or paratypes of this species and of _P. javanica_ in Calcutta. The types of Leidy's species were at one time in the collection of the Philadelphia Academy of Science.

BIOLOGY.--The zoaria of the species of _Plumatella_ are found firmly attached to stones, bricks, logs of wood, sticks, floating seeds, the stems and roots of water-plants, and occasionally to the shells of molluscs such as _Vivipara_ and _Unio_. Some species shun the light, but all are apparently confined to shallow water.

Various small oligochæte worms (e. g., _Chætogaster spongillæ_,[BG] _Nais obtusa_, _Nais elinguis_, _Slavina appendiculata_ and _Pristina longiseta_[BH]), take shelter amongst them; dipterous larvæ of the genus _Chironomus_ often build their protective tubes at the base of the zoaria, and the surface of the zooecia commonly bears a more or less profuse growth of such protozoa as _Vorticella_ and _Epistylis_. I have seen a worm of the genus _Chætogaster_ devouring the tentacles of a polypide that had been accidentally injured, but as a rule the movements of the lophophore are too quick to permit attacks of the kind, and I know of no active enemy of the genus. The growth of sponges at the base of the zoaria probably chokes some species, but one form (_F. fruticosa_) is able to surmount this difficulty by elongating its zooecia (p. 219). A small worm (_Aulophorus tonkinensis_) which is common in ponds in Burma and the east of India as far west as Lucknow, often builds the tube in which it lives mainly of the free statoblasts of this genus. It apparently makes no selection in so doing but merely gathers the commonest and lightest objects it can find, for small seeds and minute fragments of wood as well as sponge gemmules and statoblasts of other genera are also collected by it. I know of no better way of obtaining a general idea as to what sponges and phylactolæmata are present in a pond than to examine the tubes of _Aulophorus tonkinensis_.

[Footnote BG: Annandale, J. As. Soc. Bengal (n. s.) ii, p.
188, pl. i (1906).]

[Footnote BH: See Michaelsen, Mem. Ind. Mus. i, pp. 131-135
(1908).]