PHYLUM PLATYHELMINTHES 



277 



invagination, appear the suckers. When inverted this invagination 

 corresponds closely with the head and body of the cysticercoid ; 

 the bladder corresponds to the caudal vesicle. Thus the chief 

 difference between a cysticercus and a cysticercoid is that in the 



FK;. -17. Cyst of Tacnia echinococcus with the'developing'daughter-cysts and scolices. 



(After Leuckart.) 



former the caudal vesicle is relatively very large and that the order 

 of development of the parts is somewhat modified. 



A very small number both of cysticercoids and cysticerci 

 multiply by proliferation by the formation of more than one 



tape-worm head from one 

 embryo. In the few instances 

 in which this occurs among 

 the cysticercoids the hooked 

 embryo gives rise, not directly 

 to a cysticercoid, but to a 



FlR 228 Scolices of T. echinoccccus. 



(After_Cobbold.) 



FIG. 229. Separate scolex of 

 T. echinococcus. (After 

 Cobbold.) 



mass of cells from which are given off a number of buds, each 

 developing into a cysticercoid with the three parts already 

 described. One such form occurs in certain Earthworms, another 

 in a Myriapod (Glomeris limbatus). 



Tcenia ccenurus of the Dog has a bladder-worm stage in the 

 Sheep and Rabbit which gives rise to several tape- worm heads, 

 and the same holds good of Tania serialis from the Fox. But 



