XIII. 



OF THE ANATOMY AND DEYELOPEMENT OF THE 

 CYSTIC ENTOZOA * 



I. OF THE ACEPHALOCYST. 



The acephalocyst, or simple hydatid, consists of a vesicle com- 

 posed of several membranes, containing a quantity of fluid, in 

 which the young hydatids float, and from which they apparently 

 derive nourishment. 



Although found in all parts of the body, these animals are 

 nevertheless more strictly confined to the liver, which appear to 

 be their natural habitat. 



In examining an acephalocyst from without inwards, there is 

 met with, first, the natural tissues of the infested being, slightly 

 condensed, the condensation being greatest near the hydatid, and 

 becoming gradually less as the distance encreases. The next 

 part met with in the dissection inwards, is a strong fibrous mem- 

 brane, of considerable thickness, w r ith numerous blood-vessels. 

 This forms a sac for the hydatid. During the earlier stages of 

 growth, hardly a vestige of this can be seen ; for being formed of 

 the condensed tissues of the infested animal, it becomes percep- 

 tible only after the parasite has attained some size. It is highly 



* Read before the York Meeting of the British Association, 1 844. 



