MEANS AND METHODS OF REPRODUCTION 159 



though not always at the same time. The spermatozoa gradually 

 accumulate between the clitellum and the lateral surface of 

 segments 9 and 10, and then pass into the spermathecae. What 

 takes place next is uncertain so far as the earthworm is con- 

 cerned. In a related species, Eisenia foetida, the Brandling 

 worm, according to Grove and Cowley, the worms separate 

 after the spermathecae are filled and each worm forms a slime 

 tube extending from segment 7 to some point beyond the clitel- 

 lum; the portion enclosing the clitellum forming the cocoon 

 (Fig. 104). Eggs are then discharged from the oviducts and pass 

 back to the cocoon. It remains to be determined whether the 

 spermatozoa also pass back to the cocoon while the slime tube is 

 still in place or whether they are pressed 

 into the cocoon when the worm wrig- 

 gles out backward from the slime tube. 

 At any rate, the eggs are fertilized in the 

 cocoon, whose ends later contract to form 

 a closed capsule as the worm withdraws. FlG loT^pearance of 



Apparently the Supply of Sperm is not slime tube after shedding. 



exhausted in fertilizing the first batch of 



eggs, since single worms may form a number of slime tubes, with 

 cocoons, a number of times after copulation. Each of these later 

 slime tubes is shed after eggs and sperm have been deposited in 

 the cocoon (Fig. 105). 



Reproduction in the Frog. — The frog is an example of an 

 oviparous vertebrate whose eggs are fertilized externally. The 

 testes of the frog are a pair of yellow ovoid bodies, each attached 

 by a mesorchium to the dorsal body wall at the anterior border 

 of the kidneys. Spermatozoa, formed in the testis, leave through 

 a number of fine ducts, the vasa efferentia, extending from each 

 testis to the inner border of the kidney. The vasa efferentia 

 enter the kidney and open into Bidder's canal (Fig. 106), from 

 which the passageway for the spermatozoa is continued through 

 the collecting tubes of the kidney to the ureter. Near the 

 termination of the ureter in the cloaca is an enlargement, the 

 seminal vesicle, where the spermatozoa are stored until amplexus, 

 the sexual embrace, takes place, when they are discharged 

 through the cloaca. The ureter and some of the collecting ducts 

 of the kidney in the male thus serve as genito-urinary passages. 

 In the female these parts are urinary passages only. 



