LIFE HISTORY OF THE LIVER-FLUKE. 129 



however, myself met with C. tuberculata, and from com- 

 parative measurements, as well as the difference in the host, can 

 state with confidence that the species are quite distinct. And 

 even in an armed cercaria, recently found in Limnseus 

 pereger, I found cells, showing a similar arrangement, dis- 

 tinguished from the remaining cells of the body, not, indeed, 

 by coarsely granular contents, but by the possession of a pro- 

 toplasm of a finely granular nature. In this case also the more 

 granular cells are probably cystogenous. 



The other organs of the body are much obscured by the 

 presence of the opaque cystogenous cells, but the contractile 

 vesicle of the excretory system, together with the principal 

 lateral vessels, one on each side, which contain small highly 

 refractive concretions, can be made out. 



3. The Cyst. — When the snails infested with the larval 

 forms of Fasciola hepatica are kept in an aquarium, the 

 cercariae may occasionally be found swimming about in the 

 water, for the granular cells which render the body nearly 

 opaque when viewed under the microscope by transmitted light, 

 give it a snow-white appearance by reflected light, and it is 

 thus rendered conspicuous for its size. The life as a free- 

 swimming animal, however, never seems to last long, for, on 

 coming in contact with the side of the aquarium or the water- 

 plants contained in it, the cercaria proceeds to encyst itself. 

 Numbers of minute snow-white cysts may thus be seen adher- 

 ing to the walls of the aquarium or to the dark-green leaves of 

 the water-plants. The way in which the cyst is formed can be 

 readily observed under the microscope, for when examined on 

 the glass slide the cercaria soon comes to rest, and assumes a 

 rounded form, whilst a raucous substance is poured forth all 

 over the body, together with the granules forming the contents 

 of the cystogenous cells already mentioned. The tail is 

 sometimes shaken off before the encystation begins, but, as a 

 rule, the tail remains in connection with the body during the 

 process, and continues to be energetically lashed from side to 

 side, until finally a more vigorous movement detaches it. The 

 whole process of forming the cyst is very rapid, and in a few 



VOL. XXIII. NEW SER. I 



