196 ORGANISMS ILLUSTRATING RIOLOGICAL PRINCIPLES 



segments 10 and 11, and are enclosed by the ventral unpouched 

 portion of two of the three seminal vesicles. Dorsally the three pairs 

 of large pouches of the seminal vesicles in segments 9, 11, and 12 are 

 light-colored structures easily seen in a dissection. Immature sperm 

 cells are passed from the testes to complete their development in the 

 seminal vesicles. Two pairs of vasa efferentia in somites 10 and 11 

 fuse to form the paired vas deferens that carry the sperm to the 

 exterior through the male openings on segment 15. A pair of tiny 

 ovaries are attached to the anterior septum of segment 13, the eggs 



i^..-^ Semirzal rsceptocle 



--.'tes'tis 

 .--fur\T\©l 



^^..)... seminal vesicle 



ovctr^ 



ovicCuct 

 spsrm. duct^ 



Reproductive organs of the earthworm. The seminal vesicles are cut away on 

 one side to show the funnels of the sperm ducts. Read your text carefully and 

 explain how reproduction takes place. 



passing from this into the oviducts which open to the surface on seg- 

 ment 14. Fertilization of the eggs is accomplished by the process of 

 copulation in which two worms, placing themselves in opposite 

 directions, become "glued" together on their ventral surfaces by 

 means of mucus secreted from the glands of the clitellum region. 

 While they are thus placed a mutual transfer of sperm cells from the 

 seminal vesicles of one worm to the seminal receptacles of the other 

 takes place, rhythmic muscular contractions of the body helping to 

 force the sperms along. Then the worms separate. Later, when the 

 eggs are to be laid, a cocoonlike band of mucus is formed by the clitel-. 

 lum, which is forced forward by movements of the worm, and as it 

 passes by the oviducal pores, receives the ripe eggs. When it passes 

 over the opening of the seminal receptacles on the ventral surface of 



