THE FLATWORMS 



189 



string of proglottides which gradually increase in size from the 

 anterior to the posterior end. The worm may reach a length of 

 ten feet and contain eight or nine hundred proglottides. Since 

 the proglottides are budded oft from the neck (Fig. 109, B, 5), 

 those at the posterior end are the oldest. 



The anatomy of the tapeworm is adapted to its parasitic 

 habits. There is no alimentary canal, the digested food of the 



ntru-I- 



FIG. no. A proglottid of a tapeworm. 



can.excret, longitudinal excretory canals with transverse connecting vessels; 

 gl.vit, vitelline or yolk-glands; nerv.l, longitudinal nerves; ov, ov, ovaries; 

 por.gen, genital pore; schld, shell-glands; uter, uterus; vag, vagina; vas.def, 

 vas deferens. The numerous, small, round bodies are the lobes of the testes. 

 (After Leuckart.) 



host being absorbed through the body wall. A mature pro- 

 glottid is almost completely filled with reproductive organs; 

 these are shown in Figure no. 



The eggs of Tcenia solium develop into six-hooked embryos 

 (Fig. in, a) while still within the proglottis. If they are then 

 eaten by a pig, they escape from their envelopes (b) and bore 

 their way through the walls of the alimentary canal into the 

 voluntary muscles, where they form cysts (c). A head is de- 

 veloped from the cyst wall (d) and then becomes everted (e). 

 The larva is known as a bladder worm or cysticercus at this 

 stage. If insufficiently cooked pork containing cysticerci is 

 eaten by man, the bladder is thrown off, the head becomes fas- 



