104 OLIGOCHAETA 



he found that in that Annelid the male-ducts were represented by slightly enlarged 

 nephridia : an argument derived from a study of the embryology of an Enchytraeid 

 led ROULE to the same conclusion ; he states that the segments in which the male- 

 ducts will appear have no nephridia, but that the male-ducts appear rather late and 

 so suggest the idea of a pair of slightly modified nephridia which are delayed in 

 appearance in connexion with their changed function. SPENCER and I at one time 

 argued against the connexion between the excretory and genital-ducts from the ground 

 that in Perichaeta, which we believed to represent a highly archaic form, the genital 

 ducts showed no trace of their supposed origin from nephridia, the latter being 

 in a very primitive condition. SPENCER also pointed out that the genital ducts have 

 an intercellular lumen while the nephridia have an intracellular lumen ; this argument 

 is, however, at best not a strong one, and, as has been mentioned, VEJDOVSKY says 

 that the lumen in the nephridia is really also intercellular. The only positive 

 evidence as to a connexion between the nephridia and the genital- ducts has been 

 brought forward by myself. In Octochaetus multiporus the genital-ducts appear to 

 be formed out of a part of the pronephridia, thus confirming the suggestion of BALFOUB 

 (Comp. Embryol. vol. ii. p. 617) that 'in the generative segments of the Oligochaeta 

 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.' The actual facts which I brought forward upon 

 the development of the genital ducts are the following : at a comparatively late stage 

 in the development of this worm, after the pronephridia have lost their distinctive 

 character and have acquired numerous openings on to the exterior, the proximal 

 part of the nephridium which consists of the remains of the funnel (the cilia have 

 disappeared) and a straight tube leading to the body-wall separates off from the rest 

 of the nephridium ; the funnel grows and re-acquires cilia ; the tube grows into the 

 body- wall and becomes the genital duct; the genital ducts have precisely the same 

 structure at first whether they are to become oviducts or sperm-ducts ; they are, 

 moreover, only to be distinguished from the corresponding remains of the funnel 

 and the first part of the nephridium in the preceding and succeeding segments by 

 their larger size ; it should be mentioned also that there are at first traces of four 

 genital ducts in correspondence with the four gonads. It is very remarkable that 

 in the case of four pairs only of the pronephridia the commencing degeneration 

 should be arrested and growth recommence ; the tube, at first hollow, becomes solid 

 and then re-acquires a lumen ; an analogy to this state of affairs is. however, offered 

 by the occlusion (temporary) of the lumen of the oesophagus in more than one 

 Vertebrate. The disappearance followed by the reappearance of cilia upon the 



