OF THE CYSTIC ENTOZOA. 93 



compound animal. Why the pedicles of Csenurus should all 

 becdme attached to the same sac, is a fact, the cause of which it 

 will be impossible to determine with any degree of certainty ; 

 probably, however, it arises from the difference of strength in the 

 sacs of the two animals ; the greater strength of that of Csenurus 

 preventing the escape of the young gemmule 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 gem- 

 mule, 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, inherent in themselves, of attracting and assimi- 

 lating nourishment 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 enlargement of 

 these bodies resembles a process of dilatation. This, then, ap- 

 pears to be the explanation of the peculiar forms assumed by the 

 Csenurus and Cysticercus, as well as the different species of ace- 

 phalocysts ; that it is so, can be proved from Sphairidion acepha- 

 locystis, an animal very nearly allied to Csenurus, 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 containing sac. 



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

 Acephalocystis, Cffinurus, and Cysticercus, are analogous or- 

 gans ; 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 developement of Acephalocystis, 



