193 



ficially situated, it is exteriorly visible and appears as a very sinuous 

 line, extending the whole length of the sixth segment (Fig. 1). 



Dr. VON Dräsche, in his valuable monograph, very accurately 

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

 I have seen this epithelial duct opening at certain places, thus taking 

 the shape of a groove instead of that of a tube (Fig. 3). These 

 occasional imperfections of its structure, together with the peculiar 

 disposition of its constituent cells (Fig. 3, 4, 5), clearly show that 

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

 lead us also to consider it as an organ still in full course of phylo- 

 genetic development. 



Its utility, as well as the original cause of its formation, is obvious. 

 I have shown elsewhere ') that the sandy tube in which the Owenia 

 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 (Fig. 1). 

 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, which is a very long one. 



A question now presents itself: What is the morphological signi- 

 ficance 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 epi- 

 dermic 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 ofLanice conchilega, described 

 by Cunningham ^) and by 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 



1) Gustave Gilson, Les glandes filieres d. 1' Owenia fusiformis. La 

 Cellule, T. X, Fasc. 2, 1893. 



2) CtmNiNGHAM, Quart. Journ. Micr. Sc, 1888, p. 239. 



3) E. Metee, Mitt. Zool. Station Neapel, YII, 1887. 



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