Morphology of Organs. 159 



of the earthworm, the ducts are altogether independent of the 

 gonads, whose products they convey to the exterior. The 

 mouths of the ducts are at some distance from the gonads, 

 and not nearly even in contact with them. In the other type, 

 exemplified by the male ducts of the frog, the ducts of both 

 sexes in the Anodon, Periplaneta, and Astacus, the ducts have 

 the appearance of simple prolongations of the gonads. It 

 is probable, however, that this difference is not a fundamental 

 one. A consideration of the male ducts and the testes of the 

 earthworm gives the clue to the difference ; it offers an inter- 

 mediate condition' between the gonads independent of the duct 

 and the gonads continuous with their duct. In the earthworm 

 the testes are two pairs of bodies perfectly independent of the 

 ducts in the young ; later on certain sacs, the sperm sacs, are 

 formed, which envelop both testes and the funnels of the sperm 

 ducts. Thus both are enclosed in a common coelomic sac, and 

 appear to be continuous structures, an appearance which a 

 careful dissection shows not to be a reality. Now, in those 

 animals with continuous genital organs and genital ducts, there 

 is, for the most part, a reduced coelom. This is so with Anodon, 

 Helix, Astacus, and Periplaneta. In those animals it is believed 

 that the interior of the generative gland is, as already stated, 

 the remains of a part of the coelom. Hence the apparent 

 continuity of the duct with the gonad is merely an exaggera- 

 tion of the state of affairs which is found in the case of the 

 male ducts and the testes of the earthworm ; the common wall 

 enveloping gonad and duct is the wall of the coelom. As to 

 the male ducts of the frog and other Vertebrata, the continuity 

 is arrived at by secondary growths putting into connection the 

 originally distinct gonads and ducts. 



The gonad ducts themselves are usually held to have some 

 relation to nephridia. This connection is emphasized by the 

 usual way in which both systems of organs are ofteri treated in 

 the vertebrates under the general term of the genito-urinary 

 organs. As to the vertebrates, it will be clear from what has 

 been written above concerning the development of the genito- 

 urinary organs, that there is the most intimate connection 

 between the two. Ducts originally part of the excretory 



