34 THE TAPE-WORM. 



peritoneum, most assuredly meet with the same fate as if they 

 had entered the other fishes ; they will become encysted, and 

 may grow within the cysts, but will not become sexually mature 

 unless their owner be swallowed by a larger creature of his own 

 kind. 



Similar migrations and strayings from the right path are 

 exhibited by the Tania longicollis and ocellata, which are met 

 with, not only in the intestine, but also encysted in the livers, of 

 salmonoid and percoid fishes, in a jointed but sexless state. I 

 must call attention to the fact that the Tri&nophorus nodulosus, 

 in its sexless condition, is not uncommonly found in the liver and 

 peritoneum of the sticklebacks ; and as this fish, on account of its 

 spines, is generally avoided by the pike and perch, the immi- 

 grated young of the Trianophorus in the stickleback must be 

 certainly regarded as having gone astray. 



The various species of the cestoid genus, Tetrarhynchus, enu- 

 merated by systematic helminthologists, are nothing more than 

 imperfectly developed, sexless forms of Cestoidea, which, in their 

 fully developed and sexually mature condition, have been regarded 

 as belonging to an entirely distinct genus. Following Rudolphi, 

 later helminthologists termed this latter genus, Rkynchobothrium. 

 The genus Tetrarhynchus must now, however, be set aside, 

 since the forms of animals hitherto included in it must be 

 considered as younger stages of development of true Rhyncho- 

 bothria. The head end of many kinds of Tetrarhynchus, with 

 its four protractile proboscides, armed with numerous sharp 

 grappling hooks and provided with four moveable suckers, in 

 form and organization resembles so exactly the fore part of the 

 Rhynchobothria, that there is no doubt as to the origin of the 

 former. 



The Rhynchobothria in their full grown and sexually matured 

 state, are only found in the digestive canal of plagiostome fishes. 

 In order to secure their migration into other individuals of this 

 order, the young of the Rhynchobothria make use of such 

 marine creatures as serve the former for prey. As the ravenous 

 shark or ray is not over nice in the choice of its food, it is 

 not necessary for the young Rhynchobothria to select any par- 

 ticular marine animal as its temporary host, in order to introduce 

 itself into their intestine. Indeed one meets with Tetrarhynchi, 

 (that is to say young Rhynchobothria}, in soles, flounders, mullets, 



