THE ANATOMY. REPRODUCTIVE DUCTS 103 



6. Development and Homology of the reproductive ducts. 



The generative ducts of the Oligochaeta have for a long time been believed 

 to have some connexion with the nephridia, but the precise nature of this relation 

 has only quite recently been cleared up; the oviducts are more like nephridia in 

 the higher forms than are the sperm-ducts ; to begin with they occupy precisely 

 the same number of segments as does a nephridium ; the funnel opens into one 

 segment and on the segment behind this is the external pore. This is also the case 

 with the sperm-ducts of the Microdrili but not of the Megadrili. CLAPAREDE found 

 that the genital ducts in the 'Limicolae' never coincided with nephridia and thus 

 came to the conclusion that they were the modified equivalents of the latter. His 

 observations turn out, however, to have been inaccurate ; for, although in the adults 

 of the worms there are no nephridia in the segments which contain the genital-ducts, 

 the nephridia are there in the immature worms, and only disappear on the appearance 

 of the latter. The views o'f CLAPAREDE were extended to Lumbricus by LANKESTER, 

 who pointed out that there was some evidence of the primitive existence of two 

 pairs of nephridia per segment in that worm, one series being complete the other 

 represented only by the genital ducts ; the intimate relation between the nephridio- 

 pores and the orifices of the genital ducts and the setae on the other hand led to 

 this view, which was subsequently strongly supported by PERKIER. This naturalist 

 found that in some earthworms the nephridiopores were related to the dorsal instead 

 of to the ventral setae as in Lumbricus, thus showing the persistence of the presumed 

 second series of nephridia, the nephridia of Lumbricus being only partially persistent 

 in the genital ducts of those worms of which Anteus was an instance. Later PERKIER 

 found a worm (Plutellus) in which the nephridia alternated in position, now opening 

 by the dorsal now by the ventral setae; in this case, therefore, the assumption was 

 that both sets of nephridia partially persisted. The discovery of the occasional 

 coincidence of a nephridium and a genital-duct at the same seta finally led PERKIER 

 to abandon the hypothesis. This difficulty was removed by my own discovery of 

 the multiple nephridial pores of Octochaetus and other genera ; and during the progress 

 of PERRIER'S researches the discoveries of BALFOUR and SEMPER of the connexion 

 between the excretory and genital systems in the Vertebrata of course strengthened 

 the views which favoured the probability of a similar connexion in the Oligochaeta. 

 Nevertheless facts seemed to be against any such homology. The development of 

 Lumbricus showed, or appeared to show, the entire independence of the two sets 

 of structures (see BERGH 5). On the other hand STOLC, from his investigations 

 into the anatomy of the sexual organs of the genus Aeolosoma, supported the view; 



