THE TREMATODA. 89 



is little more than half developed, the two opaque ocelli, 

 characteristic of this species, appear tlirough the skin. 

 Siebold remarks, that he has found these " nursing ani- 

 mals," or germ-sacs, within other similar " nursing ani- 

 mals," or other germ-sacs, and thus it appears evident 

 to me, that the Distoma into which the C. ephemera is 

 metamorphosed, must be removed at least three genera- 

 tions from a Distoma like itself, or in other words, that 

 from its ova complete distoma-ioim& do not proceed till 

 the third generation.* 



* Since I have ventured to explain Siebold's expressions a little in ac- 

 cordance "nätk my observations, it will be proper to give my reasons for 

 doing so ; what he says with respect to the development of the " nurses" 

 is thus expressed: — " I have here and there met with a 'genn-sac' (keim- 

 scJilauch), in which I have observed among the Cercaria germs one, and some- 

 times two, or more oval, colourless bodies, furnished with a distinct pharynx 

 and a simple caecal intestine. These bodies were of nearly the same size as 

 the bodies of the Cercaria. The intestine was much convoluted, and occupied 

 nearly the whole cavity of the body. Similar oval bodies, which were evi- 

 dently to be regarded as young 'germ-sacs' (since in those which I disco- 

 vered in the ' germ-sacs' of Cercaria echinata I could clearly distinguish the 

 two posterior processes as small tubercles) presented themselves, on some 

 occasions, also in the same situation in a young Cercaria {cercarien geniste) ; 

 there might likewise be observed, by aid of the microscope, between these 

 smallest germ-sacs aud the full-grown sacs filled with embryos, some of 

 every size, so that their growth could be accurately traced, and the gradual 

 completion of the yellow, granular vesicular bodies, and of the germ- 

 granules clearly observed." (1. c. p. 190.) It is clear that Siebold met with 

 "germ-sacs" as I had with "nurses" in all stages of development, and even 

 within other " germ-sacs" which, moreover, he could not distiuguish from 

 them ; but ia these they are placed among the Cercaria germs, one, two, or 

 more together, in the form of oval, motionless bodies, of about the same 

 size as the bodies of the Cercarice. It must consequently be beheved either 

 that nurses and cercarite are developed together in one body, or that one and 

 the same creature (" germ-sac") develops both nurses and Cercarice, and even 

 simultaneously, which in my opinion would be erroneous. For it is seen 

 that the " nurses" of both species, C. ephemera and C. echinata (Sieb.) present 

 the same phenomena ; now since I have observed in hundreds of the " nurses" 

 belongiog to the latter species, that they are developed from germ-granules in 

 other " nurse" ^^^ animals, {^'parent-nurses"^ in the same way as the cercarice, 

 but that these latter never contain anything but germs of " nurses" I must 

 suppose that it is the same with the former, and am encouraged in this 

 supposition by Siebold's having met with extremely minute embryo "nurses" 

 in them ; and he expressly says that they lie not among Cercarice, but among 

 their germs, and a confounding of " nurse" -germs and Cercaria-germs may 

 occur very readily, especially when it has not been remarked that the 

 "nurses" are developed from germ-granules, as probably Siebold had not 

 happened to do. 



