568 MONTGOMERY— MORPHOLOGY OF THE [April 24, 



found in Criodrilus a pair of tubes closed internally that he called 

 Urnieren, though on account of the lateness of their origin Vejdovsky 

 considered they are rather embryonic nephridia. Wilson (1889) de- 

 scribed for Allolobophora a pair of head kidneys, and Hoffmann 

 (1899) found these opened into the head cavity. In the opinion of 

 Vejdovsky the larval nephridia develop either from the Schluck- 

 zellen, or else come from mesenchyme of ectoblastic origin. But 

 it is yet by no means decided from what germ layer these kidneys 

 originate. 



Genital Ducts. — It was Williams (1858) who first indicated the 

 homology of the genital ducts with nephridia, and he held the 

 excretory function to be secondary. Claparede pointed to the 

 typical absence of nephridia in the genital segments as evidence that 

 the genital ducts are modified nephridia. Then Lankester (1865), 

 reasoning from the condition in the Lumbricids, suggested that 

 genital ducts represent the sole traces of a ventral set of nephridia 

 that must originally have existed together with the dorsal set in all 

 the segments ; according to this view the primitive relation would be 

 two pairs of these organs to each segment. This idea was adopted 

 by Benhani (1886a, b) who maintained that in Lumhriciis, Tiianus 

 and Pontodrilus the ventral series of nephridia disappears except 

 those that change into genital organs, and that in Rhinodrilus, 

 Eudrilus, Anteus, UrochcEta and Moniligaster just the opposite con- 

 dition obtains. But Balfour (1885), as most students after him 

 concluded that one pair of nephridia to a segment is primitive, and 

 that " in the generative segments of the Oligochseta the excretory 

 organs had at first both an excretory and a generative function, and 

 that, as a secondary result of this double function, each of them 

 has become split into two parts, a generative and an excretory." 

 Here it is to be recalled that two pairs of nephridia to a segment is 

 unusual, and that only in the Lumbricidae do both genital ducts and 

 nephridia occur in the same segment ; anatomical relations therefore 

 do not bear out Lankester's theory. \\' ith regard to the embryogeny 

 of the genital ducts, Vejdovsky (1885) found them to arise inde- 

 pendently of the nephridia, though he considered they might be 

 wholly or in part homodynamous with the latter; at least the funnels 



