EARTHWORM 



235 



Lincoln, Nebraska, their burrows have been followed to a depth of more 

 than 18 feet from the surface. In winter they usually remain below 

 frost line. 



275. Reproductive System and Reproduction. — Both sets of sex 

 organs (Fig. 139) are present in each individual earthworm, this animal 

 being monecious. The male organs include three pairs of seminal 

 vesicles, the first two of which open into a common central reservoir in 

 the tenth metamere and the third into a similar reservoir in the eleventh 

 metamere. In each reservoir is found a pair of testes. From each 

 reservoir vasa efferentia lead into a common vas deferens on each side, 

 the outer opening of which is in metamere XV. The sperm cells are 

 produced in the testes, matured in the seminal vesicles, and passed out 

 through the vasa efferentia and vasa deferentia. 



Uerve corc^ 



Fig. 139. 



SetrJi'na/ 

 recepfac/es 



— Testis 



3e/T7i'na/ 

 ves/c/es 



Ovary 



Ovtcfact 



Vas deferens 



-Reproductive organs of an earthworm. (From Wieman, "General Zoology," 

 by the courtesy of McGraw-Hill Book Compa7iy, Inc.) 



The female organs consist of a pair of ovaries in metamere XIII. 

 The egg cells are set free in the coelom and on each side are collected by 

 a ciliated funnel which leads into an oviduct in metamere XIV; this opens 

 to the outside on the ventral surface of this metamere. In addition 

 there are two pairs of seminal receptacles in the ninth and tenth meta- 

 meres, which open to the outside in the grooves between the ninth and 

 tenth, and the tenth and eleventh, metameres. 



Self-fertilization does not take place in the earthworm, but sperm 

 cells are transferred from one individual to another by a process of 

 copulation. Two worms come together with their ventral surfaces in 

 contact and with their anterior ends pointed in opposite directions (Fig. 

 140 A), placing themselves so that metameres IX, X, and XI of one 

 worm are opposite the clitellum of the other. They are held together 

 by two slime tubes formed from mucus secreted by the clitellar and other 

 skin glands, each tube extending from metameres IX to XV of one worm 



