58 PHYLUM ANNELIDA 



tion of the animal, being largest during periods of sexual activity. 

 (2) The testes. Two pairs of these organs are present, which He 

 beneath the sperm sacs in the tenth and eleventh somites ; they 

 are very minute objects and will not be seen. (3) The sperm ducts. 

 These are a pair of slender white tubes which extend from the 

 sperm sacs to the fifteenth somite, where they open, through the 

 conspicuous transverse slits already noticed, to the exterior. Look 

 first for the posterior portion of these tubes and trace them for- 

 ward. The spermatozoa pass from the testes, where they but 

 partially develop, into the sperm sacs, in which their development 

 is completed and where they are grouped together in balls. From 

 here they pass, during pairing, into the sperm ducts, and out of 

 the animal through the slitlike openings in the fifteenth somite. 



The Female Organs, (i) The sperm receptacles. These are two 

 pairs of spherical white sacs beneath the sperm sacs in the ninth 

 and tenth somites ; they are easily seen. (2) The ovaries. These 

 are a pair of extremely small organs lying near the median line 

 and attached to the anterior septum of the thirteenth somite 

 near the ventral body wall ; they will hardly be seen. (3) The 

 oviducts. These are two minute, funnel-shaped tubes which 

 extend from immediately behind the ovaries through the septum 

 to the external opening in the next somite ; they will also hardly 

 be seen. 



During the months of May and June earthworms meet and 

 pair in the nighttime. Two animals place themselves along- 

 side of each other, headed in opposite directions and in such a way 

 that the sperm receptacles of each come opposite the openings of 

 the sperm ducts of the other, and are held firmly together by the 

 secretion of glands in the integument. The sperm receptacles 

 of each are then filled with spermatozoa from the other animal. 

 The worms then separate. Sometime later the clitellum secretes 

 a viscid fluid which hardens and forms a tough, cylindrical mem- 

 brane around the body. The worm then squirms backward, caus- 

 ing this membrane to pass forward toward its head. As the 

 membrane passes the fourteenth somite, eggs are poured from 

 the oviducts into the viscous mass which is held between it and 

 the body, and at the tenth and eleventh somites spermatozoa pass 



