114 



INVERTEBRATE ZOOLOGY 



the body surface. The excretory system is highly characteristic. 

 This consists of a series of finely branching tubes following a 

 definite pattern of arrangement distinctive for each family of 



flukes. At the posterior 



end of the body the tubes 

 empty into a median blad- 

 der. Each collecting tubule 

 terminates distally in a 

 flame cell the most charac- 

 teristic feature of which is a 

 tiny tuft of cilia extending 

 into the lumen of the tube. 

 In the adult worm (Fig. 

 66 A), the male reproduc- 

 tive organs consist normally 

 of two testes which com- 

 municate with the genital 

 pore through the vas 

 deferens and a cirrus. The 

 female organs comprise an 

 ovary of variable form from 

 which an oviduct leads 

 through a modified region 

 called the ootype into the 

 uterus. Between the ovary 

 and the ootype the oviduct 

 may receive two canals, one 

 from the vitelline receptacle 

 and the other from the 

 Laurer's canal and the 

 receptaculum seminis. As 

 ova pass from the ovary 

 down the oviduct, sperma- 

 tozoa from the receptacu- 

 lum seminis and yolk and 

 shell material from the vitel- 

 line receptacle pass with 

 them into the ootype. Here 

 each fertilized ovum and a number of yolk cells become sur- 

 rounded by a shell to form an egg. The ootype is a modified 

 portion of the oviduct in the region of the so-called shell gland 



Fig. 64. — Photograph of a sheep-liver 

 fluke stained and cleared for microscopic 

 study. (Orig.). 



