92 MANUAL OF ANIMAL BIOLOGY 



Wastes from the blood, present in the tiny vessels running to the 

 nephridia, may also, perhaps, be removed to some extent by the 

 nephridial cells, but it appears clear that the chloragogen cells, 

 which come into intimate contact with the blood in the intesti- 

 nal vessels, are the most important excretory agents of the blood. 

 It is usually held that such wastes eventually find their way into 

 the coelomic fluid through the disintegration of the chloragogen 

 cells, although some authorities have concluded that the wastes 

 remain permanently in these cells. 



5. Reproductive System 



The Earthworm possesses a complicated set of organs for 

 sexual reproduction, and since each worm possesses both male and 

 female organs, it is an hermaphroditic animal just as is Hydra. 

 The reproductive organs in the Earthworm, however, are much 

 more highly developed than are those of the Hydra. In the first 

 place, they are permanent organs, and, in the second place, the 

 reproductive system of the Earthworm is greatly complicated by 

 the presence of an elaborate arrangement of accessory structures so 

 that sperm from two animals may be exchanged in order to bring 

 about cross-fertilization, that is, the fertilization of the eggs of one 

 animal by the sperm of another. (W. f. 60.) 



Male Organs of Reproduction. These consist of (a) two 

 pairs of testes situated close to the ventral body wall and attached 

 to the anterior septum of segments x and xi. The testes consti- 

 tute the essential part of the male organs of reproduction, for it is 

 in them that the sperm are formed. Each pair is enclosed by a 

 special fluid-filled cavity in the coelom, the testis sac, developed 

 ventrally in segments x and xi. 



(6) A pair of sac-like seminal vesicles is found in segments 

 ix, xi, and xii, making three pairs in all. The seminal vesicles 

 are directly connected with the testis sacs ; those in ix and xi with 

 the sac in x, and the pair in xii with the sac in xi. The sperm are 

 formed primarily in the the testes, but before they are mature they 

 are released into the enclosing testis sacs and thence into the sem- 

 inal vesicles. Here they remain for a time and undergo final 

 development. Finally, they are again passed into the testis sacs, 

 and then into the openings of the sperm ducts for passage to the 

 exterior. 



(c) A pair of sperm ducts open externally, one to the right 



