27 



before the female. Male organs: testes, efferent ducts, vas deferens, 

 cirrus, or -penis, penis sac. Female organs: ovaries, oviduct, yolk 

 gland, shell gland, uterus, receptaculum seminis. Ripe proglottids 

 have sex organs, except enormously enlarged uterus, atrophied; 

 are little more than sacs of eggs, of which it is estimated that there 

 may be as many as 50,000 in each. Terminal proglottids break off 

 and pass out with feces. 



Life history — Independent life of the free proglottid; scattering 

 of the eggs ; the six hooked embryo taken up with food by hog or man ; 

 migration of the embryo from the alimentary canal of its host (swine 

 or man) to the muscles or other organs; formation of cysts, "measles" 

 each containing the invaginated head of the future tapeworm, (the 

 Cysticerus stage). Development of the adult from the cystic state. 

 Possibility of autoinfection renders T. solium a dangerous species. 



Interpretation of structure and life history — Two views; 1st, that 

 there is a true alternation of generations, the tape-worm representing 

 a linear colony of which the proglottids are the sexual individuals, 

 produced by budding from an asexual scolex. 2d, that it is to be 

 regarded as a segmented individual, comparable to an Annelid. 

 Anatomical facts opposed to "colony" theory. According to second 

 theory, the formation of proglottids a process of accelerated re- 

 generation. 



Frequency of occurrence in man — Relation to food habits. Very 

 uncommon in U. S. Confusion with T. saginata. 



Prevention — Avoiding imperfectly cooked pork; meat infection. 



Other species infesting man in this country — T. saginata, the 

 beef tape- worm; Hymenolepis nana; Echinococcus granulosus, adult 

 in dogs; Dipylidium caninum, normal host, dogs; Dibothriocephalus 

 lotus, larva in fish. 



Dipylidium caninum — {Taenia cucumerina). Commonest para- 

 site of pet cats and dogs. Occasionally in children. Size small, 

 15-30 cm. Structure, head with retractile rostellum, 4 rows of hooks; 

 proglottids resemble cucumber seeds in shape; two genital pores and 

 double sets of sexual organs. 



Life history — Eggs in capsules. Larva a cysticercoid, parasitic in 

 dog louse or dog flea. Transfer by dog biting infested fleas. Infec- 

 tion of humans by accidental ingestion of an infested flea, (see 

 Blanchard, '07). 



