l82 AN INTRODUCTION TO ZOOLOGY 



wall, one pair in somite IX, the other in somite X. They open 

 to the outside through the spermathecal pores between somites 

 IX and X, and X and XI. 



MALE ORGANS (Fig. 93). The male reproductive organs are 

 two pairs of glove-shaped testes (T), one pair in somite X, the other 

 in somite XI. They occupy positions in the somites similar to 

 that of the ovaries. Behind each testis is a ciliated funnel (SF) 

 shaped like a rosette; this is the opening of the sperm duct or 

 vas deferens (VD). This duct passes through the septum just 

 back of the funnel, forms several convolutions, and then extends 

 backward near the ventral surface. The two sperm ducts arising 

 on either side of the mid- ventral line unite in somite XII and then 

 run back as a single tube, opening to the outside through the 

 spermiducal pore on somite XV. In a sexually mature earth- 

 worm, the testes and funnel-shaped inner openings of the sperm 

 ducts are inclosed by large white sacs, the seminal vesicles (A, 

 B, C), lying in somites IX to XII. There are three pairs of 

 these sperm sacs, one in somite IX (A), one in somite XI (C), 

 and the third in somite XII. In somites X and XI are central 

 reservoirs (B). 



COPULATION. Many of the events which precede the laying of 

 eggs by the earthworm have not yet been learned. Reproduc- 

 tion is best known in the common manure worm, Allolobophora 

 fcetida. The breeding season begins early in the spring and con- 

 tinues until late in the autumn. Sexually mature worms possess 

 a much swollen clitellar region. Although both eggs and sperms 

 are produced by every individual, self-fertilization does not take 

 place, but the eggs of one worm are fertilized by the sperm of 

 another. The sperm are transferred from one worm to another 

 during a process called copulation, which usually takes place 

 just beneath the surface of the earth. Two worms come together 

 with their heads in opposite directions, and their ventral surfaces 

 opposed, as shown in Figure 94, A. Each secretes about itself 

 a tube of slime which extends from about the eighth to the thirty- 

 sixth somite. Four bandlike thickenings, probably of the slime 



