PHYLUM PLATYHELMINTHES 



(vas.def.). Eggs arise in the bilobed ovary (ov) and pass into 

 a tube, the oviduct. Yolk from the yolk-gland (gl.vit) enters 

 the oviduct and surrounds the eggs. A chitinous shell is then 

 provided by the shell eland (schld) and the eggs pass into the 

 uterus (uter}. The eggs have in the meantime been fertilized 

 by spermatozoa, which probably co'me from the same proglottis, 

 and move down the vagina (vag). As the proglottides grow 

 older the uterus becomes distended with eggs and sends off 

 branches (Fig. 107,*), while the rest of the reproductive organs 

 are absorbed. The ripe proglottides break off and pass out of 

 the host with the faeces. 



The eggs of Tcenia solium develop into six-hooked embryos 

 (Fig. 109, a) while still within the pro- 

 glottis. If they are then eaten by a pig, 

 they escape from their envelopes (Fig. 

 109, b) and bore their way through the 

 walls of the alimentary canal into the 

 voluntary muscles, where they form cysts 

 (Fig. 109, c). A head is developed from 

 the cyst wall (Fig. 109, d) and then 

 becomes everted (e). The larva is known 

 as a ffiff^^,-%s?(y w _.QL cysticercus at this 

 stage. If insufficiently cooked pork con- 

 taining cysticerci is eaten by man, the 

 bladder is thrown off, the head becomes 

 fastened to the wall of the intestine, and 

 a series of proglottides is developed. 



FIG. no. A uniseg- 

 mental cestod, Archigetes 

 sieboldii, from the coelom 

 of a worm, Tubifex 

 rivulorum. app, persist- 

 ent larval appendage; 

 go, genital pore; hk, per- 

 sistent larval hooks ; 

 ov, ovary ; sc, sucker ; 



adult stage. The body consists of a head te, testes; yg, yolk- 



or " scolex " followed by a chain of similar 



joints or " proglottides " which are budded tory, after Leuckart.) 



b. Cestoda in General 



The CESTODA are all ento parasitic flat- 

 worms, called tapeworms ; they inhabit 

 the alimentary canal of vertebrates in the 



