476 ANATOMICAL AND PATHOLOGICAL OBSERVATIONS. 



XXXIII. OF THE ANATOMY AND DEVELOPMENT 

 OF THE CYSTIC ENTOZOA .* (PLATES VI. X. XI. XII.) 



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 ap- 

 parently derive nourishment. 



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

 nevertheless more strictly confined to the liver, which appears 

 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 increases. 

 The next part met with in the dissection inwards, is a strong 

 fibrous membrane, of considerable thickness, with numerous 

 bloodvessels. 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 perceptible only after the parasite has 

 attained some size. It is highly vascular, and forms a cushion, 

 to which the external surface of the hydatid is applied. In 

 this way, a steady supply of the blood, or of debris of the 

 textures of the infested animal, is close at hand, from which 

 the hydatid may extract nourishment. This membrane is 

 best seen in aged hydatids, or in those in which the process 



* Read before the York Meeting of the British Association, 1844. 



