1*90.] (lenital Ducts and Nephridia in the OligochfKta. 453 



total independence of the two structures in Lumbricus and those 

 iiqaatic Oligochoeta of which the development is known is a difficulty 

 iu the way of accepting this view. Claparedo, who first clearly 

 formulated the arguments in favour of regarding the genital dui-ts 

 as slightly modified nephridia, made a mistake in stating that the 

 genital segments of the aquatic Oligochneta contain no nephridia; 

 this error was pointed out by Vejdovsky* who discovered that the 

 genital segments are originally furnished with nephridia, which 

 atrophy on the ripening of the sexual products and the appearance of 

 their ducts. Professor Lankester pointed out that in Lumbricus^ the 

 genital ducts and the nephridia have a close relation to one 

 or other of the two pairs of setae with which each segment is pro- 

 vided. He suggested that the genital ducts might represent the only 

 portion left of a ventrally opening series of nephridia. M. Perrier's 

 memorable investigations^ into the structure of exotic Earthworms 

 tended at first to confirm this theory. He discovered that in one 

 Earthworm (Plutellus) the nephridia alternated in position from 

 segment to segment, thus suggesting that the supposed original two 

 sets of nephridia had both partly persisted and partly disappeared. 

 In other forms the nephridia were found to be related to the ventral 

 setae, and the genital apertures to the dorsal setae, the exact converse 

 of the condition which occurs in Lumbricus. Later investigations, 

 however, which resulted in the discovery that the genital apertures 

 and nephridi^pores may coincide at the same seta, led M. Perrier to 

 abandon the hypothesis. My own discovery, first published in the 

 Proceedings of this Society, that in Acanthodnlus multiporus there 

 are more than a single pair of nephridiopores to each segment, 

 removed the difficulties urged by Perrier. And as this discovery has 

 been extended by myself and by others to many species and genera 

 of Earthworms, there can be no longer any intrinsic improbability in 

 the hypothesis. The whole subject has been lately reviewed by Eisig 

 in his treatise upon the Anatomy and Physiology of the Capitellidae, 

 which forms one of the series of monographs issued by the Zoological 

 Station at Naples. Dr. Eisig decides that the genital ducts arc 

 probably modified nephridia in the Oligochseta; in the Capitellidae 

 they certainly are; but, as the Capitellidae do not appear to me to be 

 so nearly related to the Oligochseta as Dr. Eisig considers, I should 

 regard this argument as only having the force that an argument 

 from analogy can have. Since the appearance of Dr. Eisig's work, 

 an important paper by Dr. Stolc|| dealing with the generative organs 



* ' System u. Morph. d. Oligochaten,' Prag, 1884. 

 f ' Quart. Journ. Microsc. Sci.,' 1864-5. 

 J ' NOUT. Arch, du Museum,' vol. 8 (1872). 

 ' Roy. Soc. Proc.,' vol. 38, 1885, p. 459. 

 j| ' Boiim. Oesell. Sitzber.,' 1889. 



