I20 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



During life the penis is often moved backward and for- 

 ward within the genital atrium, or becoming relatively slen- 

 der, its tip may be protruded through the external opening. 

 In captivity this is not a frequent occurrence, but that it 

 does occur is an undoubted fact. In rarer cases the fibers 

 traversing the prostate reservoirs contract, and thus com- 

 pressed the prostate secretion is forced through the penis, 

 and in some cases out of the opening of the genital atrium. 

 Here it remains undissolved, showing furrows formed by 

 wrinkles in the walls of the genital atrium and giving evi- 

 dence of being a thick and viscous substance. 



The vas deferens enters the walls of the prostate reser- 

 voir at the constriction between its two lobes (fig. 13). 

 From here it passes forward imbedded in the thick wall of 

 the same side, and opens into the lumen of the penis at the 

 summit of a minute papilla visible in living specimens. 

 This included section is usually distended with sperm, 

 and is probably homologous with the ductus ejaculatorius 

 in other species of trematodes. 



V. The Female Reproductive System. 



The ovary, double convex in form, is situated in the 

 median line a short distance anterior to the testes (fig. 

 II, 13, ov.^. The enclosing sheath in all essential respects 

 resembles that of the testes. Immediately beneath this the 

 germ cells are usually minute, and constitute a growth zone 

 from which the developing ova migrate, increasing in size 

 as they pass inward. There are also from one to upwards 

 of a dozen small groups of cells scattered throughout the 

 ovary. These groups consist of cells of various sizes, some 

 of which may rarely be found to be in the process of divi- 

 sion. The fully formed ova are characterized by a well 

 defined cell membrane, the absence of yolk, a large 

 nucleus, and especially large nucleolus. 



Outside of the egg-laying period, the oviduct, consisting 

 of spongy protoplasm containing numerous nuclei but de- 

 void of definite cell boundaries, may readily be traced from 

 about the center of the ovary to a point on its anterior 



