74 DEVELOPMENT OF 



closely allied to Distoma, changes its form in this way, 

 and by doing so acquires a remarkable similarity to the 

 " nurses' and ''' parent nurses' of the genus Bistoma, the 

 course of whose development I have endeavoured to 

 exhibit, and since this progeny in consequence of its 

 metamorphosis rather becomes more unlike the form of 

 the parent animal than approaches it, it will surely not be 

 considered too bold to assume, tJiat the animals which are 

 the immediate result of the metamorphosis, do not by 

 another transformation become actual Monostomata, but 

 that they develop the germs which do eventually become 

 perfect Monostomata, or in other words, that these meta- 

 morphosed young ones are to be considered as " nurses J" 

 If we now introduce a link such as we have presented 

 to us by the Monostomata, into the series of develop- 

 ment of the Distomata given above, the whole cycle will 

 be completed, and as I should hope organically completed 

 or nearly so. Several examples of the same kind will be 

 presented in what follows. 



((5) Ceecaria armata, Siebold. 



(Tab. üi. fig. 1—6.) 



As I am obliged by want of space to be as brief as 

 possible, I shall refer as much as I can to the figures 

 and to the communications of Siebold respecting this 

 species,* as I have no doubt but that the one I have 

 before me is the same with that described by him — 

 although in this case, Wagner's figure referred to in 

 Oken's ' Isis,' (1834, ii, tab. 2,) is not quite correct, — and 

 because I think that figures will give a much more correct 

 idea of the animal than a lengthened description. 



This Cercaria is scarcely half the size of the former 

 one, but is equally lively and active in all its parts ; 

 though it has not the power of rolling itself into a ball 

 when swimming in the water, and the tail does not on 



* In Burdacli's Pliysiologie. 2(1 edit, toni, ii, p. 187, scq. 



