TiENIA EOHINOCOCOUS. 



263 



have two distinct membranes ; an outer, thick, laminated, homoge- 

 neous elastic layer (the edocyst of Huxley), and an internal, thin, 

 soft, granulated, compai^atively inelastic layer — the endocyst of 

 the same author. As these terms are extremely convenient and 

 simple, I shall frequently employ them. Histologically, the 

 ectocyst is structureless, consisting of a substance closely allied 

 to chitine ; for this and other reasons it is not unfrequently 

 called the cuticular layer ; the endocyst, on the contrary, is the 

 essential vital part of the animal, representing, according to my 

 ideas of morphology, a huge compound caudal vesicle. In an 

 example from the zebra, Huxley found that it was " not more 

 than ^0 of an inch in thickness, being composed of very dehcate 

 cells of 2^" to siloo' in diameter, without obvious nuclei ; but often 

 containing clear, strongly refracting corpuscles, generally a single 

 one only in a cell." Huxley adds : " 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 process, and sometimes the corpuscles are not acted 



Fig. 57.— Two Echinococcus scoliees, from an hydatid developed in the liver of a sheep ; treated 

 with acetic acid, and slightly compressed (X 220 diam.)— Busk. 



upon at all by the acid, appearing then to be of a fatty nature. A 

 strong solution of caustic ammonia produces a concentrically 

 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." In consequence of 



