206 



THE ANIMAL PARASITES OF MAN 



Sooner or later the oncospheres of tapeworms come to rest, 

 and are first transformed into small cysts, which may be round or 

 oval according to the species. The embryonal hooks disappear sooner 

 or later, or remain close together or spread over some part of the 

 cyst (fig. 134, b). Their discovery by v. Stein in the bladder-worm 

 of the larva of Tenebrio molitor first led to the conclusion that the 

 cysticerci actually originate from the oncospheres of Tseniae. 



The cyst may remain as a cyst, and then by proliferation the 

 scolex forms within it (fig. 136), or it may divide into an anterior 

 cystic portion and a solid tail-like appendix of various length, on 

 which the embryonal hooks are. to be found, and this is particularly 



FIG. 134. Cysticercoid of Avion ater. 50/1. (a] In the contracted condition. 

 (b) In the extended state with the embryonal hooks maintained, and with 

 water vessels, &c. 



the case in regard to those species of Taenia (cysticercoids) that 

 develop in invertebrate animals, such as arthropoda. 



As mentioned above, the scolex is understood to be an 

 individual that originates through proliferation of the wall of the 

 parent cyst, mostly singly, but in those cystercerci that are termed 

 Cce-nurus (fig. 135) many occur, whereas in the cysticercus stage of 

 Echinococcus the parent cyst originating from the oncosphere of 

 Tcenia echinococcus (of the dog) first produces a number of daughter 

 cysts, which in their turn form numerous scolices. Echinococcus- 

 like conditions also occur in cysticercoids, as, for instance, in 

 those peculiar to earthworms ; and similar conditions prevail in a 



