492 ANATOMICAL AND PATHOLOGICAL OBSERVATIONS. 



mule from between its membranes. The mode of formation 

 of the sac is also a point interesting to the physiologist, and 

 one deserving consideration. In Acephalocystis and the other 

 allied genera, the original gemmule, shortly after it has become 

 an independent animal, begins to swell out and be distended 

 from the accumulation of new matter within it. This new 

 matter is drawn into it by means of the young internal cells 

 which have just been formed, and which have a power, in- 

 herent in themselves, of attracting and assimilating nourish- 

 ment from without. The cells referred to here are the young 

 germs of future hydatids, and which afterwards, as already 

 explained, become independent animals ; but, at the same 

 time, there is in many cases also another series of cells, whose 

 only function is to act in this way, and throughout the term of 

 their existence : these have been termed absorbent cells. 

 Now, these cells drawing in the nourishment in this way 

 cause the expansion of the original cell-wall, so that the en- 

 largement of these bodies resembles a process of dilatation. 

 This, then, appears to be the explanation of the peculiar forms 

 assumed by the Caenurus and Cysticercus, as well as the 

 different species of acephalocysts ; that it is so can be proved 

 from Sphairidion aceplialocystis, an animal very nearly allied 

 to Caenurus, and being a connecting link between the acephalic 

 and cephalic hydatids ; for in this animal we find that portion 

 of its body analogous to the pedicle of Cysticercus, not exserted, 

 as in the latter animal, but situated in the centre of the body, 

 where it forms the attracting point for the nourishment 

 absorbed, which accordingly dilates the external and con- 

 taining sac. 



What I wish to be inferred from this is, that the sacs of 

 Acephalocystis, Caenurus, and Cysticercus, are analogous 

 organs ; and that the pedicles of these two latter animals are 

 analogous to the reproductive nucleus, which may be observed 

 during certain early stages of the development of Acephalo- 



