114 THE EARTHWORM 



efferentes, the partially differentiated male germ cells upon leaving the 

 testes do not at once enter the funnels, but pass into the lobes of the 

 seminal vesicles. There they complete their differentiation, and the 

 mature spermatozoa are then ready to enter the ductus efferentes and 

 so pass to the outside through the ductus deferentes. The four testes 

 and the four funnels have, therefore, a relation to the ccelom similar 

 to the ovaries and their oviducts. The seminal vesicles, by enclosing 

 both testes and funnels in a common cavity, prevent the spermatozoa 

 from escaping into the coelom and furnish a cavity in which sperma- 

 togenesis is completed. Compare the relationship to the ccelom of these 

 male and female ducts with the relationship to the coelom of the 

 nephridia. In many annelids the nephridia function as the reproduc- 

 tive ducts. 



(i) The seminal receptacles, which should not be confused with the 

 seminal vesicles, are small whitish bodies attached to the ventral body 

 wall on each side in the region of somites 9 and 10. They open to the 

 outside only, and their function is to receive the spermatozoa obtained 

 from another worm during sexual union. 



(j) Consult a model, or a figure of the entire reproductive system, 

 and then construct a large semidiagrammatic figure showing all these 

 parts. Review their relationships by tracing the course of the ova and 

 spermatozoa from gonads to the external openings of the oviducts and 

 ductus deferentes. 



(k) Cut out one of the ovaries and transfer to a slide. Add a drop 

 of glycerin, put on a cover glass, and study under the low-power ob- 

 jective. The female germ cells will be seen in various stages of growth 

 and differentiation. Where are they most advanced? The largest 

 ones show a nucleus and nucleolus. Recall the stages of development 

 of the ova in ovary of the frog. Make a drawing of the entire ovary, 

 6 cm. in length. 



(1) Understand from lectures and textbook the functioning of the 

 various parts in sexual union and egg-laying. Examine again the 

 clitellum and the markings that extend forward from this glandular 

 area to the openings of the ductus deferentes and the external openings 

 of the oviducts. 



Exercise 7. — The Nervous System. 



(m) Lift the posterior end of the pharynx with forceps, and cut the 

 muscles that connect it with the body wall. Trace the nerve cord 

 anteriorly and find where it divides into right and left branches, the 

 circumpharyngeal connectives, which encircle the pharynx and unite in 

 the dorsal ganglia. Look for nerves from the brain and from the 



