THE TREMATOD A, 61 



have allowed of alteration by contraction and expansion. 

 The digestive organs occupied their usual position ; but 

 tln-ough the integument they appeared only like a uni- 

 formly coloured, structureless material filling a forked 

 cavity, at the upper end of which might be observed a 

 pore, surrounded vdth a distinct border. The organs 

 containing globules, situated on each side of the middle 

 line, could at this time be traced upwards towards the 

 mouth, only for about half their length. 



We have now seen, that the Cercaria echinata is de- 

 veloped into an actual ßuJce or Distoma. When I first 

 became acquainted with these remarkable creatures, I had 

 no doubt of the identity of the ßuke, (fig. 8 e and fig. 

 8 /,) with the Cercaria echinata (fig. 6 ;) but it was not 

 till the last winter that I met vdth individuals which 

 having just quitted the pupa cases, were about to pene- 

 trate into the body or glandular organs of the snail 

 (fig. % a b c d). Those in the condition represented in 

 (fig. 8 e and/,) occurred only in the liver, and indeed in 

 that portion which occupied the outermost whorls of the 

 shell. 



The fm'ther advance of this ßuke to a fully developed 

 animal, as we know it, may perhaps be determined from 

 consideration of the other Distomata and Monostomata, 

 in which the first stage of development has been shown 

 by the observations of Siebold and others. Our present 

 information would lead us to conclude that it deposits ova, 

 from which, either within the maternal body or without 

 it, oval-shaped young proceed, which move about briskly 

 in the fluid contained in the interior of the snail, or in 

 the smTounding water, and bear no resemblance to their 

 parent. In what way this progeny is transformed into a 

 ßuke, or as we now know into a Cercaria, is as yet an 

 unexplained mystery ; but that this change can and does 

 take place throughout, only by the intervention of several 

 generations, may be assumed as beyond doubt ; and if we 

 examine attentively what is taught us by Bojanus, Baer, 

 and Siebold, respecting the development of the Cercarice, 



