380 Zoological Society. 



adherent to the last-descrihed layer of the ectocyst, but may, with 

 great care, be separated from it, when it is at once evident that 

 there is no organic connexion between the two ; this layer may be 

 very conveniently termed the endocyst — it is the only active living 

 part of the whole wall of the cyst, and represents the proper body- 

 wall of the animal. It is very pale and delicate, and not more than 

 2"^cjo^ n °f an ulcn thick. It is composed of very delicate cells -g-oVo - 

 ■g-^oo-th of an inch in diameter, without obvious nuclei, but often con- 

 taining clear, strongly refracting corpuscles, generally a single one 

 only, in a cell. These corpuscles appear to be solid, but by the action 

 of dilute acetic acid, the interior generally clears up very rapidly, and 

 a hollow vesicle is left of the same size as the original corpuscle. No 

 gas is developed during this j»'ocess, and sometimes the corpuscles 

 are not acted upon at all by the acid, appearing then to be of a fatty 

 nature. A strong solution of caustic ammonia produces a concen- 

 trically laminated or fissured appearance in them. Under pressure, 

 and with commencing putrefaction, a number of them sometimes flow 

 together into an irregular or rounded mass. 



The inner surface of the endocyst is sometimes irregularly papil- 

 lated like a glandular epithelium in consequence of the prominence 

 of separate cells, or its surface presents an even contour, from the 

 presence of a structureless membrane, which varies in thickness, and 

 seems to represent the inner portion of the blastema, elsewhere 

 slightly granular, in which the cells are imbedded. 



Solitary hooks are scattered over the inner surface of the endocyst. 

 I thought at first that they had fallen from the Echinoeocci ; but it 

 is with some difficulty that, even by the aid of pressure, the hooks 

 can be so detached from them ; and furthermore the hooks in question 

 had generally the appearance of those forms found in the younger Echi- 

 nococci, from which there is still greater difficulty in detaching them. 

 I conclude then that these hooks are developed where they are found, 

 and that they represent a sort of attempt to develope an Echinococcus 

 which has gone no further. Within the substance of the endocyst 

 one may see here and there traces of clear delicate vessels, such as 

 those which will be described in the secondary cysts ; but probably 

 in consequence of the granular nature of the membrane, they are 

 rarely visible. 



In describing the development of the Echinoeocci, it will be neces- 

 sary to return to this endocyst — at present I pass to the contents of 

 the cyst. This is a clear, colourless, serous liquid, in which two 

 kinds of bodies are found floating, a. Echinoeocci, and b. secondary 

 cysts. 



a. Echinoeocci. To avoid circumlocution, I restrict this term in 

 the present place to what are commonly called the Echinococcus- 

 heads. 



The Echinoeocci are minute, oval bodies, varying, according to the 

 state of contraction in which they are found, from s^-- g^th of an 

 inch in their long diameter. 



When fully extended, the Echinoeocci are divided by a constriction 

 into two portions ; an anterior somewhat conical part, and a posterior 



