Chapter VIII: Introduction: Description of the Polyclad Leptoplana Tremellaris (3)

The worm is found usually in couples, which have been proved to be male and female individuals (Fig. 34), often in considerable numbers in the veins of the pelvic region, chiefly the veins of the bladder and of the large intestine, and it is tolerably certain that _Bilharzia_ enter these vessels from the portal vein. Their long slender bodies enable them to penetrate into the finer vessels, which get partially or entirely choked up, and the circulation accordingly impeded. But the most serious consequences are observed in the urinary bladder. The mucous membrane is swollen and inflamed here and there, chiefly on the dorsal surface, the capillaries appear varicose and covered with mucus, mixed with blood-extravasations in which _Bilharzia_-eggs are noticeable. The eggs also cause numerous swollen knots in the submucous tissue. Should the disease not pass beyond this stage (and such is usually the case, especially in South Africa), a temporary haematuria ensues. The urine, which is only expelled with great effort, accompanied by intense pain, is mixed with blood, mucous clots, and masses of _Bilharzia_-eggs, from which some of the embryos have already hatched out. The symptoms, however, may gradually pass away, and a more or less complete recovery accomplished. The disease may indeed be of a far less severe character, and may not interfere with the usual occupations of the patient; but, on {70}the other hand, a far more extensive thickening of the wall of the bladder sometimes occurs; hard masses of eggs, uric acid crystals, and other deposits, may lead to the formation of stones, degeneration of the substance of the ureter, and eventually to that of the kidney itself. The stone, indeed, has long been known to be a prevalent disease in Egypt, and it is now known to arise from concretions formed round masses of _Bilharzia_ eggs. From the portal vein, again, other _Bilharzia_ may gain access to the rectum, or the liver, and it has also been found in the lungs, and may give rise to most serious complications, if indeed the patient lives.

How infection occurs is a question to which at present no satisfactory answer can be made. The attempt to introduce embryos of _Bilharzia_ into the common fresh-water animals of Alexandria has hitherto proved fruitless (Looss[88]), although there seems little doubt that the comparative immunity of Europeans from the disease is in some way owing to their drinking purer water than the natives. Possibly, as Leuckart suggests, the embryo becomes a sporocyst in man himself, somewhat as _Taenia murina_ is known to develop in the rat without an intermediate host.[89] The immense numbers of the parasite in one host would then readily receive an explanation.

A _Bilharzia_, possibly _B. haematobia_, was found by Cobbold in the portal vein of _Cercopithecus fuliginosus_; and _B. crassa_ infests the cattle of Egypt, Sicily, and certain parts of India, but does not produce haematuria.

Of the other Trematodes of man and domestic animals there is not room to speak fully. _Distomum pulmonale_, which occurs in the lungs of the cat, tiger, and dog, as well as in man, is especially common in Japan, China, Corea, and Formosa. _D. sinense_ and _D. rathouisi_ have been also found in inhabitants of these countries.

BISEXUAL TREMATODES.—Zoologically, _Bilharzia_ is interesting from its bisexual condition. It is not, however, the only bisexual Trematode. In cysts in the branchial chamber of Ray's bream, _Brama raii_, two worms are found, which are probably the slender male and the swollen female of the same species (_Distomum okenii_). The only doubt that can arise proceeds from the tendency in all Trematodes for the male organs to ripen before {71}the female organs. Until we certainly know that the swollen egg-bearing form (♀) does not arise from a previously male form (♂), the case is open to suspicion. Since, however, Kölliker[90] never found intermediate hermaphrodite conditions, this _Distomum_ may be almost certainly regarded as of distinct sexes. _Didymozoon thynni_ (_Monostomum bipartitum_), from cysts on the gills of the Tunny (_Thynnus_), is another case. Two slender worms flattened posteriorly, come together, and the body of one becomes folded to receive that of the other. They fuse completely except for a small lateral opening through which the anterior parts of both worms may freely protrude. The enclosing individual contains a coiled uterus filled with eggs, and is the female, whereas the smaller individual never possesses eggs, and is probably the male.[91] _Nematobothrium_ (Fig. 22, A), which occurs also in the Tunny, in the form of two immensely long individuals intricately wound about each other in a cyst, is, however, not bisexual.

TABLE OF DIGENETIC TREMATODES AND THEIR LIFE-HISTORIES.[92]

Host into which the Host into which the
larva enters, and in Cercariae migrate and
Species. Final host. which Cercariae are encyst; eaten by
eventually formed. final host.

_Diplodiscus_ Smaller species Insect-larvae, _Rana_,
(_Amphistomum_) _Rana_, _Bufo_, of _Planorbis_ _Bufo_, but frequently
_subclavatus_ _Triton_ and _Cyclas_ omitted
Göze

_Distomum advena_
Duj. _Sorex araneus_ Not known _Limax_
(_D. migrans_ Duj.)

_D. appendiculatum_ _Clupea alosa_ Not known _Lucullus acuspes_,
Rud. _Centropages hamatus_
(Copepoda)

_Limnaea
_D. ascidia_ Species of Bats stagnalis_ _Ephemera_, _Perla_,
v. Ben. _Planorbis _Chironomus plumosus_
corneus_

_D. atriventre_ Frogs and Toads _Physa heterostropha_
Weinl. of N. America Not known

_D. brachysomum_ The Dunlin Not known _Anthura gracilis_
Crepl. (_Tringa alpina_)

_D. caudatum_ Hedgehog _Helix hortensis_
v. Linst. (_Erinaceus europaeus_)

_D. clavigerum_ _Limnaea ovata_ Not known {72}
Rud. _Rana_ _Planorbis corneus_

_D. cygnoides_ _Pisidium_, _Limnaea_ sp.
Zed. _Rana_ _Cyclas_ (_Cercaria macrocerca_
Fil.)

_D. cylindraceum_ _Limnaea ovata_
Zed. _Rana_ _Ilybius fuliginosus_

_D. dimorphum_ _Ardea_, Different species of
Dies. _Ciconia_ Not known Fishes
(Brazil)

_D. echinatum_ _Cygnus_, Species of Species of _Limnaea_,
Zed. _Anser_, Limnaea _Paludina vivipara_
_Anas_

_D. endolobum_ _Rana_ _Limnaea _L. stagnalis_,
Duj. stagnalis_ _Gammarus pulex_,
larvae of
_Limnophilus rhombicus_

_Limnaea stagnalis_,
_L. ovata_,
_D. globiporum_ Not known _Succinea pfeifferi_,
Rud. _Perca fluviatilis_ _S. putris_,
_Physa fontinalis_,
_Planorbis marginatus_

_D. hepaticum_ Sheep, Oxen, _Limnaea truncatula_
Abild. Man, etc. Omitted

_D. hystrix_ _Lophius piscatorius_ Marine Fishes
Duj. Not known

_D. macrostomum_ Warblers, Tits, Omitted
Rud. Woodpeckers, etc. _Succinea putris_

_D. militare_ Common Snipe _Paludina vivipara_ _P. vivipara_
v. Ben.

_D. nodulosum_ _Bithynia tentaculata_ _Cyprinus_,
Zed. _Perca fluviatilis_ _Acerina cernua_

_D. ovocaudatum_ Species of _Planorbis_ Probably omitted.
Vulp. _Rana esculenta_ (_Cercaria_ known
as _C. cystophora_
Wag.)

_D. retusum_ _Rana_ _Limnaea stagnalis_ _L. stagnalis_, larvae
Duj. of Phryganeidae

_D. squamula_ Polecat Unknown _Rana temporaria_
Dies.

_D. signatum_ _Tropidonotus Unknown _Rana_
Duj. natrix_

_D. trigonocephalum_ _Paludina vivipara_
Rud. Badger, Polecat Unknown

Dogfish, Rays _Ostrea edulis_, _Belone vulgaris_
_Gasterostomum_ sp. _Cardium rusticum_,
_C. edule_

_Unio_, _Anodonta_
_G. fimbriatum_ (_Cercaria_ known _Leuciscus
v. Sieb. _Perca_, _Esox_ as _Bucephalus erythrophthalmus_
polymorphus_)

_G. gracilescens_ Unknown Species of _Gadus_
Rud. _Lophius piscatorius_ (e.g. _G. aeglefinus_),
_Molva_, _Lophius_

_Monostomum flavum_ _Planorbis corneus_
Mehl. _Anas_ Omitted

CLASSIFICATION OF TREMATODES.—We have seen (p. 63) that it is hardly possible to carry out fully the division of Trematodes into Monogenea and Digenea. Nevertheless, pending further investigation on the doubtful points, this classification may still be {73}used. Monticelli[93] has proposed the main divisions of a new classification, which has been also adopted by Braun, and is based on the nature of the suckers. These divisions are indicated below in brackets.

A. MONOGENEA v. Ben. (HETEROCOTYLEA Mont.).
1. Fam. TEMNOCEPHALIDAE Hasw.
Gen. _Temnocephala_ Hasw.
2. Fam. TRISTOMATIDAE Tschbg.
Sub-Fam. 1. Tristomatinae Mont.
Gen. _Tristomum_, _Nitzschia_, _Epibdella_, _Trochopus_,
_Acanthocotyle_, _Phyllonella_, _Placunella_,
_Encotylabe_.
Sub-Fam. 2. Monocotylinae Tschbg.
Gen. _Pseudocotyle_, _Calicotyle_, _Monocotyle_.
Sub-Fam. 3. Udonellinae v. Ben.-Hesse.
Gen. _Udonella_, _Echinella_, _Pteronella_.
3. Fam. POLYSTOMATIDAE Tschbg.
Sub-Fam. 4. Octocotylinae v. Ben.-Hesse.
Gen. _Octobothrium_, _Pleurocotyle_, _Diplozoon_,
_Anthocotyle_, _Vallisnia_, _Phyllocotyle_,
_Hexacotyle_, _Platycotyle_, _Plectanocotyle_,
_Diclidophora_.
Sub-Fam. 5. Polystomatinae v. Ben.
Gen. _Polystomum_, _Onchocotyle_, _Erpocotyle_,
_Diplobothrium_, _Sphyranura_.
Sub-Fam. 6. Microcotylinae Tschbg.
Gen. _Microcotyle_, _Gastrocotyle_, _Axine_, _Pseudaxine_.
4. Fam. GYRODACTYLIDAE v. Ben.
Sub-Fam. 7. Gyrodactylinae Par. et Per.
Gen. _Gyrodactylus_, _Dactylogyrus_, _Tetraonchus_,
_Diplectanum_.
Sub-Fam. 8. Calceostominae Par. et Per.
Gen. _Calceostomum_, _Anoplodiscus_.
5. Fam. ASPIDOBOTHRIDAE Burm. (= Aspidocotylea Mont.).
Gen. _Aspidogaster_, _Platyaspis_, _Cotylogaster_,
_Macraspis_.

B. DIGENEA v. Ben. (MALACOCOTYLEA Mont.).
6. Fam. HOLOSTOMATIDAE Brandes (= Metastatica Leuckart).
Gen. _Diplostomum_, _Polycotyle_, _Hemistomum_,
_Holostomum_.
7. Fam. AMPHISTOMATIDAE Mont.
Gen. _Amphistomum_, _Diplodiscus_, _Gastrodiscus_,
_Homalogaster_, _Gastrothylax_, _Aspidocotyle_.
8. Fam. DISTOMATIDAE Mont.
Gen. _Distomum_ (and sub-genera), _Rhopalophorus_,
_Koellikeria_, _Bilharzia_.
9. Fam. GASTEROSTOMATIDAE Braun.
Gen. _Gasterostomum_.
10. Fam. DIDYMOZOONTIDAE Mont.
Gen. _Didymozoon_, _Nematobothrium_.
11. Fam. MONOSTOMATIDAE Mont.
Gen. _Monostomum_, _Notocotyle_, _Ogmogaster_,
_Opisthotrema_.

{74}CHAPTER III

CESTODA