694 REPORT — 1894. 



Although my own researches are far from terminated, I am aWe to give some 

 information on the subject. 



In fact, the nephridial system is not altogether absent, but is in a state of 

 extreme reduction and seems to have lost all secretory function. It consists 

 usually of one pair, sometimes two pairs, of very small funnels, lying in the 

 posterior part of the sixth segment, against the muscular layer, in an extremely 

 dorsal position. 



Each of these funnels ends in a very thin tube, which passes through the 

 muscular coat ; but, instead of opening directly and freely on the epidermic 

 surface, these tubes fall into a longitudinal duct which runs forward and opens, 

 through a tiny pore, at the other end of the sixth segment. 



This duct is a merely epithelial structure ; it lies outside of the thick basal 

 membrane, within the epiderm itself. Being thus superficially situated, it is 

 exteriorly visible, and appears as a very sinuous line, extending the whole length 

 of the sixth segment. Dr. von Drasche, in his valuable monograph, very accu- 

 rately represented this line, though he did not make out its significance. 



1 have seen this epithelial duct opening at certain places, thus taking the shape 

 of a groove instead of that of a tube. These occasional imperfections of its 

 structure, together with the peculiar disposition of its constituent cells, show that 

 this canal originates as a longitudinal folding of the epithelium. They lead u» 

 also to consider it as an organ still in full course of pbylogenetic evolution. Its 

 utility, as well as the original cause of its formation, is obvious. I have shown 

 elsewhere that the sandy tube in which the Oioenia lives is rather tight round the 

 fore end of the body. The genital products could scarcely reach the exterior were 

 they directly ejected into the space between the worm and its protective sheath. 

 The animal is obliged to protrude its body out of its dwelling, but, thanks to the 

 epidermic canal, it is spared the trouble and danger of laying bare more than its 

 five anterior segments, though the funnels lie in the posterior part of the sixth. 



A question now presents itself: What is th^ morphological significance of 

 this epidermic duct ? 



It is not my intention, in the present state of my researches, to enter into a 

 full discussion of the subject. I shall content myself with calling attention to the 

 bearing which the discovery of the epidermic canal of Owenia may have on the 

 discussion of the homologies of the excretory system in general. 



We know other instances of a longitudinal duct in connection with the 

 nephridia. The most classical one is that of Lanice conchilega, described by 

 Mr. Cunningham and Dr. E. Meyer. 



The longitudinal duct of this species is generally regarded as an unsegmented 

 part of the longitudinal row of cells which gives origin to the excretory system — an 

 opinion which I have no reason to oppose. 



But certain morphologists go further than that, and compare the longitudinal 

 duct of Lanice, Polymmia, Polygordius, and others to the segmental canal or primi- 

 tive ureter of vertebrates. Professor Wilson, in his remarkable paper on the germ- 

 bands of Lwnbricus, goes even so far as to consider this homology as evident. 



On this point I venture to recall attention to Professor Haddon's hypothesis 

 as to the pbylogenetic origin and epiblastic nature of the segmental duct of 

 vertebrates. 



The existence of such an evidently adaptive structure as the epidermic duct of 

 Oiuenia seems to give a remarkable confirmation to his suggestion as to how a 

 continuous groove into which the nephridia opened may have been converted into 

 a canal. 



It is not evident at all that the segmental duct really Is, in its whole length, 

 an unsegmented part of a cell-row homologous to that of Clepsine or Lumhricus. 

 It may have appeared at a much later period of the pbylogenetic evolution, and 

 have been, at a given moment, a new structure corresponding to new wants, just 

 as the epidermic duct of Ojcenia corresponds to a peculiar disposition of the pro- 

 tective tube of the worm. The coexistence of a segmental duct analogous to the 

 epithelial duct of Owenia, and of a structure homologous to the longitudinal canal 

 of Lanice, is even possible. 



