ENTOZOA. 77 



infested by the B. auriculatus is a carnivorous fish {Mustehis vul- 

 garis), inhabiting the same sea as the Eledone moschata, and prone 

 to devour that and other kinds of cuttle-fishes. The fertile ova of 

 the B. auriculatus are discharged by thousands from the molluski- 

 vorous fish, and thousands of the larvas doubtless perish. Some, 

 however, gain an entry into the interior of the lower organised 

 marine animals suited to their further development and encysted 

 life ; still fewer complete their vital career when the, to them, lucky 

 accident occurs of the devouring of the mollusk containing them by 

 the fish whose intestines form a suitable nidus for their ultimate 

 transformation, and for the development and propagation by spon- 

 taneous fission of the generative segments. 



Another cestoid larva found in cuttle-fishes and other marine 

 invertebrata is characterised by its four lateral elliptical suckers, the 

 tumid borders of which are facetted, or divided by many incisions. 

 The Bothnocephalus coronatus, " bothriis tumidulis transversim 

 costatis," of Rudolphi, presents the like peculiarities of its suckers, 

 and it is found in the intestines of fishes that feed upon the inverte- 

 brates and smaller fishes in which the larva in question (^Scolex 

 polymorphus, Auct.*) is found. 



To take a final instance, indicative of the migration of the cestoid 

 larvae, from land animals. The common tapeworm of the cat, 

 Tcsnia crassicollis, is remarkable for the disproportionate size of the 

 head, the short and thick neck, the position of the four suckers, and 

 the shape and number of the booklets of the uncinated proboscis : all 

 these peculiarities are repeated in the larval form of tape-worm 

 which is commonly developed in cysts of the liver of the mouse and 

 rat, and which has already been described as the Cysticercus fascio- 

 laris. The warm blood and high organisation of the small mammal 

 in which that larva is developed may well be regarded as favouring 

 a further advance of that development than takes place in the en- 

 cysted cestoid larvae found in the cold-blooded invertebrates; and 

 accordingly we find, not only the uncinated proboscis and suckers of 

 the tapeworm established, but also a lengthening and segmentation 

 of the body, in the so-called Cysticercus of the rat, without, how- 

 ever, the development of the generative organs, and with a tendency 

 to a dropsical accumulation of nutrient fluid in a few of the terminal 

 joints. 



All cestoid larvae which find their early entrance into the soft tissues 



* LL t.xi. fig. 10. The cestoid larvae, in their various grades of development, 

 have served as the gronnds of many nominal genera of entozoa ; e. g. Antkoce- 

 phalus, Balanophorus, Bothriocephalus bicolor, Dibothriorhynchus, Floriceps, Gymno- 

 rhynchus, Hepatoxylon, Rhynchobothrium, SccHex, Tentacvlaria, and Tetrarhynehus. 



