The Nematode parasites of the Invertebrata are usually immature forms which attain their full development in the body of some vertebrate; but there are a number of species which in the sexually adult condition are peculiar to the Invertebrata.2 The Nematoda contain about as many parasitic species as all the other groups of internal parasites taken together; they are found in almost all the organs of the body, and by their presence, especially when encysted in the tissues and during their migration from one part of the body to another, give rise to various pathological conditions.
The adult worm, which is of extremely minute size, the male being only Fi l sth and the female s of an inch in length inhabits the alimentary canal of man and many other carnivorous mammalia; the young bore their way into the tissues and become encysted in the muscles - within the muscle-bundles according to Leuckart, but in the connective tissue between them according to Chatin and others.
Here it becomes encysted, and losing its boring apparatus and claw-bearing processes remains for a time quiescent.
The size of the animals varies greatly, from forms a few millimetres in length to Gigantorhynchus gigas, which measures from 10 to 65 cms. The adults live in great numbers in the alimentary canal of some vertebrate, usually fish, the larvae are as a rule encysted in the body cavity of some invertebrate, most often an insect or crustacean, more rarely a small fish.
The adults occur in Elasmobranch fish, the metacestode encysted in Teleosts.
Schistostomum (Bilharzia) haematobium in which the male is larger than the female and encloses the latter in a ventral canal; Koellikeria filicolle Rud (Distomum okenii, K01l) which also occurs in pairs, a large female and a small male being found together encysted in the branchial chamber of Brama raja: and Didymozoon thynni (Monostomum bipartitum) which occurs in pairs fused for the greater part of their length and only free anteriorly; the larger individual is the female.
Humilis in North America: and is eaten by sheep during its encysted stage attached to herbage.
In this condition they remain encysted as immature flukes until eaten by their final host.
A comparison Linguistic ever, occupied the greater part of lands both north and south of Panama; the others were encysted in the territory of the prevailing families, or concealed in cols-de-sac of the mountains.
Here it becomes encysted, and is nourished by the exudations of the fish.
The mollusc reciprocates by throwing off its embryos on the parent fish, in the skin of which they remain encysted for some time, the period of reproduction of the fish and mussel coinciding.
In some cases these organs are retained, in some they are lost in the encysted condition.