PLATYHELMINTHES 



79 



" head " or scolex armed with both hooks and suckers. The pro- 

 glottids are budded from the neck, the oldest being at the posterior 

 end. The worm may reach a length of over twelve feet and have 

 1,000 proglottids. 



An alimentary canal is not necessary on account of the parasitic 

 habit of absorbing food predigested. Excretory tubes end in flame 

 cells. 



The complete reproductive system develops in each of the pro- 

 glottids and attains sexual maturity beginning with the 200th. 

 The animal is male nearer the anterior end and hermaphroditic 

 posteriorly. The male structures consist of testes, efferent ducts, 

 vasa deferentia, a cirrus and a cirrus sac. 



The female reproductive system consists of the paired ovary, 

 the oviduct, yolk gland and duct, shell gland and duct and the uterus 

 and vagina. The uterus is simple until the 600th segment; then it 

 branches. 



The egg rises in the ovary, passes into the oviduct, and is included 

 with the yolk cells and spermatozoa in a chitinous shell, and finally 

 passes into the uterus and is released by rupture of the uterus when 

 the matured segment is discharged. Fertilization takes place before 

 the shell is formed, and may be by sperms from the same proglottid. 

 The eggs develop into hexacanth (6 hooked) embryos while still in 

 the uterus. They pass out in the feces and if eaten by a pig escape 

 from their covering and bore into the muscles. A proscolex, which 

 is a cyst with the cavity filled with water, develops a head and forms 

 a bladder worni or cysticercus with the scolex invaginated into the 

 bladder. When infested pork which is not fully cooked is eaten, 

 man receives cysticerci, which evert and attach, by the scolex, to the 

 wall of the alimentary canal and develop a chain oi proglottids. 



Cestode Parasites. — Echinococcus granulosus {Taenia echino- 

 coccus) is found in the intestine of the dog. It is the most injurious to 

 man of the parasites belonging to the Cestode group and is taken into 

 the body upon unwashed salads or in drinking water contaminated by 

 ova from infected dogs. The adult worm in the dog has usually not 

 more than four or five proglottids. When the eggs reach the ali- 

 mentary canal of man, cattle, sheep, and hogs, the egg shells are 

 dissolved and the hooked embryos bore into the liver where they 

 develop into cysts. The bladder-worm stage is extremely large, 

 sometimes reaching a diameter of seven inches. It produces a large 

 number of scolices which in turn produce other crops of scolices. 



