T^NIA ECHINOCOCOUS. 263 



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

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

 soft, granulated, comparatively inelastic layer — the endocyst of 

 the same author. As these terms are extremely convenient and 

 simple, I shall ft-equently employ them. Histologically, the 

 ectocyst is structureless, consisting of a substance closely allied 

 to ohitine ; 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, accordiag to my 

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

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

 than 2m of an inch in thickness, being composed of very dehcate 

 cells of 2^" to 5^" 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 



■pxa. 57. Two Echinococcus scolices, 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 



