118 A. p. THOMAS. 



other hand, were present in almost all fairly developed ex- 

 amples ; in form they most closely resembled the ciliated open- 

 ings in Clepsiue complanata, as figured by Leydig. The 

 vessel was opened on one side and expanded into a two-horned 

 lobe, covered on its inner surface with cilia. In short, the 

 ciliated opening was described as similar to the inner ends of 

 the segmental organs of various annelids. I have never found 

 the sporocysts which Thiry studied, but it seems improbable 

 that there should be any great difference in the structure of the 

 ciliated ends in question in the various species of sporocysts. 

 The isolated cilia really present are very large and their motion 

 peculiar, so that it is not difficult to understand that any one 

 who had before his mind the segmental organ of the earthworm, 

 and was not prepared to see a large isolated cilium within an 

 infundibulum, might take the waves passing along the cilium 

 for waves travelling over a series of small cilia. There can be 

 no doubt, therefore, that the ciliated infundibula have essen- 

 tially the same structure in the asexual generations (sporocysts 

 and rediae) as in the adult sexual trematodes. 



Amongst the digenetic trematodes the reproduction of sporo- 

 cysts by sporocysts takes place, either by transverse fission, 

 which may be continued through several generations, as in the 

 case of Cercaria limacis, or by the formation of sporocysts 

 within the parent, or both methods may occur in the same 

 species (e. g. Cercaria chlorotica, &c.). But the only way in 

 which the sporocysts are multiplied in the case of Fasciola 

 hepatica is by transverse division, and this is of far less 

 frequent occurrence than in some other species of trematodes. 

 There appears to be a great and invariable increase of the 

 nurse-forms amongst the Distomidse, and in Fasciola 

 hepatica the multiplication is effected by the production of 

 numerous broods of the more highly organised rediae. Fission 

 does, however, sometimes occur, and usually at an early stage 

 in the growth of the original sporocyst. A constriction 

 appears about the middle of the body, and becomes deeper 

 and deeper (fig. 9), and finally the two halves are completely 

 severed. One of these contains the remains of the head- 



