190 ANIMAL PARASITES. 



inner vesicle gradually separates from its enveloping cyst. If such 

 a cyst be cut through, the gelatinous, very elastic wall of the cystic 

 worm separates from the cyst at these cut places, and rolls itself 

 up, when with a forceps it may easily be separated in its whole 

 extent from the inner wall of the cyst, in which case the worm 

 furnishes a true representation of any inequalities in the outer 

 cyst. 



As regards the structure of the walls of the true Echinococcus- 

 vesicle, it is characterised by the following circumstances, which 

 must be accurately estimated, on account of Acephalocysts : 



1. The walls are extraordinarily elastic, and tremble, like 

 jelly, when touched, even after they are empty, which we do not 

 see in the walls of a Cysticercus. 



2. The walls of such a vesicle never collapse entirely, as is 

 the case in the Cysticerct, nor do they lie, like these, after 

 death, flat at the bottom of the envelope-cyst, but even when 

 dead they still adhere to particular spots in the envelope-cyst, 

 in which case an adhesion takes place between the latter and 

 the worm as if by plastic exudation. 



3. The cut margins of such cysts roll themselves up, which 

 gives them a gaping appearance. 



4. The transverse section of the walls of such a cystic worm 

 distinctly shows a structure consisting of more or less numerous 

 consecutive circular strata, varying according to age, which we 

 find merely indicated in dead Cystic, tenuicolles, and in so low a 

 degree that it requires considerable practice to detect even very 

 slight indications of such lines. 



With regard to the structure of this Cestode, Eschricht says 

 that the walls consist of two similar membranes, which are only 

 loosely connected, and of which the outer one is of a cartilaginous 

 nature, and the other, which is thin and smooth, has the texture 

 of a mucous membrane, is large enough to bear an epithelium 

 (which Von Siebold, as I think rightly, denies), and beset with 

 small elevations of a size up to %" ' } which are partly very young 

 scolices in the act of development, partly further developed 

 scolices of jo'", and partly, according to Eschricht, representing 

 the points on which such scolices formerly sat. In the fluid con- 

 tained in these vesicles there are also free scolices, part of Avhich 

 are still furnished with the remains of the stalk, and which, on 

 the application of pressure, form flat discs with the outline of an 

 apple cut down the middle ; from the hinder third of this, 



