454 PARASITES OF ANIMALS 



eyes, but other forms of trematode Iarva9 are furnished with 

 visual organs. Accordingly, I never found eyes in young 

 distomata whilst they were in their last dwelling-place, but eyes 

 are certainly present in the young forms of Polystoma and 

 Amphistoma. The supposition that a spontaneous wandering 

 is associated with eyes is not yet confirmed in my experience. 



" (h). As a means of distinguishing the different forms of 

 Cercarias, amongst other indications, their places of dwelling 

 may be useful, because each mollusk only harbors a limited 

 number of species. Notwithstanding, Professor Filippi is in 

 error if he believes that every species of mollusk carries only a 

 single armed form of cercaria. A migration of the cercaria is 

 indispensable to its perfection. 



" (i). Many larval trematodes form cysts round themselves, 

 probably by means of a special organ of secretion, and also by 

 the epidermis. Their future destiny necessitates this. The 

 sporocysts apparently fulfil towards the larvae, which are deve- 

 loped within them, a similar purpose, namely, a protection 

 against the stomachal digestion of the new host. In the pupa 

 condition the development of the larva, which has now thrown 

 off the tail, makes greater or less progress, according as to 

 whether it is surrounded by nourishment or not. In particular, 

 while in this stage, the different kinds of hooks for migratory 

 purposes make their appearance, always, without doubt, after 

 the shedding of the skin. Other trematodes pass through this 

 tail-less sexually-immature stage without any cyst. I have not 

 yet seen any larval trematode forms which had been produced 

 in sporocysts or rediae without appendages ; they appear to 

 occur, nevertheless. 



" (k). As the larvse exist only in a few hosts and most of 

 them dwell only in one species of animal so, also, the con- 

 tinued progress towards sexual maturity only succeeds in the 

 case of certain well-defined larval organisms, but the digestion 

 of the cysts and liberation of the larvae may be accomplished in 

 various animals. 



" (/). The armed Cercariae appear to be larvae of the spine- 

 covered distomes of amphibia ; for, as examples, the Cercaria 

 ornata becomes transformed into Distoma clavigerum, and C. 

 armata into Distoma endolobum ; the Dist. duplicatum and 

 Gere, diplocotylea are, apparently, the juvenile forms of Dist. 

 cygnoides and Amphistoma subclavatum. The Dist. echiniferum 

 of Paludina could neither be advanced in development in the 



