A TAPEWORM. 29 



canals, respectively. Transverse connections of this sort, as well 

 as longitudinal cords and canals themselves, are usually to difficult 

 of demonstration for an exercise of this kind. 



g) At one side of the proglottid note the genital pore. Extruding 

 from this pore, or perhaps withdrawn into it, is the cirrus. 



h) Leading back from the genital pore into the mass of the proglottid is 

 a convoluted tube, the vas deferens, and a less tortuous canal, the 

 vagina. 



i) The vas deferens connects outwardly with the cirrus and by numer- 

 ous interior branches with the scattered testes. The latter are 

 small round bodies or groups of bodies occupying, at this stage, the 

 bulk of the proglottid. 



j) The vagina joins the genital pore and a point just below the uterus. 

 The latter, when not distended with eggs, appears as a straight tube 

 in the middle of the proglottid. 



k) Posterior to the uterus are the two ovaries, large round or oval- 

 shaped masses. 



1) Close to the posterior border of the proglottid is an irregular mass of 

 lobules forming the yolk gland, and between this and the end of 

 the uterus another, smaller mass, the shell gland. The secretions 

 or products of these glands, together with the ova from the ovaries, 

 are discharged into the inner end of the vagina and from there pass 

 by a duct into the uterus. 



DEVELOPMENT. Each proglottid of a tapeworm possesses a full 

 set of reproductive organs, both male and female, and is hi reality, ther- 

 fore, a hermaphroditic individual. Cross fertilization between two 

 proglottids of the same or different tapeworms may, however, occur. 

 When ripe, so to speak, the proglottids break off from the posterior 

 end of the string and pass from the host. In time the eggs from these 

 proglottids may, by the vicissitudes of chance, find their way into the 

 food or drinking water of other animals and be taken into the alimentary 

 tract of the latter. In the intestine of this intermediate host the eggs 

 hatch. The larvae now migrate to certain tissues, mentioned before, 

 where they become encysted. No further development is ever attained 



