192 



ZOOLOGY. 



suitable animal they break from their cysts, bore through the wall of the 

 digestive tract into the tissues. Here they grow, become encysted and at 

 this stage develop, in anticipation of the needs of the adult worm, the head 

 or scolex which remains attached to the bladder-like cyst (Fig. 91, A, B). 

 Development stops at this point unless the flesh of this host is eaten by 



FIG. 92. 



FIG. 92. Diagram of a sexually mature proglottis of Tania. A, anterior end; e, 

 embryos; ex., excretory canals; g.p., genital pore; ov., ovaries (paired); r.s., recep- 

 taculum seminis; s.g., shell gland; t, testes; ut., uterus filled with embryos; v, vagina; 

 v.d., vas deferens; y.g., yolk gland. 



Questions on the figure. Why is self-fertilization possible in tape- 

 worm? What is the function of the various portions of the reproductive 

 apparatus? Trace the following steps and indicate where each incident 

 happens : formation of eggs and sperm ; passage of sperm to vas deferens 

 and into vagina ; storing of sperm in receptaculum seminis ; fertilization 

 in the oviduct; addition of yolk; ovum covered with the shell secretion; 

 passage into uterus where development proceeds. 



some other animal. When this happens the bladder is thrown off, the 

 head becomes attached to the wall of the intestine of the carnivorous host, 

 and the active formation of the chain of proglottides begins again. The 

 more common Tape-worms of man are Tcenia solium and Tcenia saginata. 

 The former is more common in Europe and is received into the system 



