CROSSOBOTHRIUM LACINIATUM. 41 



middle of the animal, and just anterior to the testes. Lying 

 against it is the sac-like ootype, into which the ovary opens. 

 From the posterior end of the ootype the long, coiled, duct- 

 like uterus passes backward to near the posterior end of the worm, 

 turns and passes forward, and finally opens at a point on the 

 ventral surface near the male opening. The uterus of an adult 

 worm usually contains embryos and fills the body, so as to ob- 

 scure the other parts. 



The vitellaria consist of numerous small, rounded masses that 

 lie near the margins of the animal. The products of these organs 

 are emptied into the ootype through a short common duct, just 

 ventral to the ootype. Do you know what they are for? Laurer's 

 canal is a short duct which leads from the ootype to the exterior. 

 Its function is doubtful. 



CESTODA. 



The Cestoda are endoparasites which possess very few of 

 those organs that are characteristic of free-living animals. They 

 have no alimentary canal, no organs of special sense, and, 

 except in the head, the nervous system is feebly developed. 

 On the other hand, the organs needed for the reproduction of 

 the species are enormously developed, so that in the more mature 

 portions of the animal, the ovaries, testes, and accessory organs 

 occupy nearly the whole space. Can you explain why this is 

 true? 



CROSSOBOTHRIUM LACINIATUM. 



This form passes its adult life in the intestine (spiral valve) 

 of the sand-shark. Cestode larvae which may be the young of 

 this species are abundant in the cystic duct of the squeteague. 

 How the developing eggs and embryos are conveyed from the 

 shark to the squeteague is not known. The transfer of the 

 larvaB from the squeteague to the alimentary canal of the shark 

 can be easily understood. 



Adult Stage. 1. Notice specimens that are attached to the 

 wall of the intestine of the shark. 



