THE ANATOMY. REPRODUCTIVE DUCTS 



103 



§ 6. Bevelopment 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 cleai-ed 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 of Claparede were extended to Lumbricus by Lankestee, 



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 genita.1 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 Peeeier. 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 ffenital ducts of those worms of which Anteus was an instance. Later Peeriee 



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 Peerier 



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 Perrieb'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 Beegh 5). On the other hand Stolc, from his investigations 



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



