DEVELOPMENT OF THE TAPEWORMS 



303 



When the infection has been intense, and the body is crowded with numerous 

 oncospheres, acute feverish symptoms, are induced, to which the infected animals 

 usually succumb (" acute cestode tuberculosis ") ; while in other cases the alterations 

 in the organs attacked as the liver in mice and the brain in sheep may cause death. 



Sooner or later the oncospheres of tapeworms come to rest, 

 and are first transformed into a bladder, which may be round or 

 oval according to the species. The embryonal spines disappear sooner 

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

 bladder wall (fig. 200). Their discovery by v. Stein in the bladder 

 worm of the " meal worm " (the larva of a beetle, Tenebrio molitor) 

 first led to the conclusion that bladder worms (cysticerci) actually 

 originate from the oncospheres of Tceniidcv. 



FIG. 200. Diagram of development of a cysticercus. I, solid oncosphere with six spines ; 

 2, bladder formed by liquefaction cf contents ; 3, invagination of bladder wall ; 4, formation 

 of rostellum (with booklets) and suckers -at the bottom of the invagination ; 5, evagination of 

 head; 6, complete evagination effected by pressure. (Stephens.) 



The bladder may remain as a bladder, and then by proliferation 

 the .scolex forms on its wall (fig. 202), or it may divide into an 

 anterior so-called "cystic" portion and a solid tail-like appendage of 

 various lengths, on which the embryonal hooks are to be found, 

 and this is particularly the case in those larval forms (cysticercoids), 

 e.g., those of Dipylidium caninum, that develop in invertebrate animals, 

 such as Arthropoda. 



As mentioned above one may regard the scolex as an individual 

 that originates through proliferation of the wall of the parent cyst, 

 mostly singly, but in those cysticerci that are termed ccenurus 

 (fig. 201) many scolices occur, whereas in those called echinococcus 

 the parent cyst originating from the oncosphere of Tcenia echinococcus 

 (of the dog) first produces a number of daughter cysts, which in their 



