one to two vaginal openings which are located in different positions either on 

 the ventral side or along the sides, or on the dorsal side of the body and 

 may be located both at the level of the ovary and closer to the anterior end 

 or, on the contrary, to the posterior end of the body. Thus, among mono- 

 genetic trematodes the number of external pores of the sex system fluctu- 

 ates from one to four. In addition to that, among many forms, predominantly 

 the more highly organized ones, there is a special duct of the sex system 

 which connects it to the digestive system (see pageVl ). 



The sex atrium, (atrium genital e communae) (Fig. 78) is pre- 

 sent among a number of monogenetic trematodes and in the simplest cases 

 represents a small cavity separated from the external medium by a narrow 



03mm 



Fig. 78. Microcotyle sebastis G oto, 

 sagittal section through the body of 

 the worm in the region of the sex 

 atrium. Enlarged 245 times 

 (According to Goto, 1894). 



Fig. 79. Parancyrocephalus daicoci 

 Yamaguti, adult worm. (According 

 to Yannaguti, 1938). 



part and resulting from a drawing -in of the exterior cuticle and often 

 equipped with special musculature. Into this sex atrium the uterus opens 

 more ventrally, and the male sex system also opens somewhat closer to 

 the dorsal surface. Along with such simple structure of the atrium con- 

 siderable complications occur. Often the common atrium forms two more 

 or less well-developed concavities into which sex ducts open. The common 



50 



