ME, FRANK E. BEDDARD ON THE ANATOMY OF OCNERODRILUS. 569 



In my species I find that, as Eisen has discovered, there are (fig. 3h) two pairs of 

 specially dilated perivisceral vessels, but that they lie in segments X and XI instead of 

 IX and X. A comparison with Limnodrilus is thus rendered less valid. In Microscolex 

 and Photodrilus there are three pairs of such vessels — in X, XI, and XII, and it is 

 rather with these that I should be disposed to compare Ocnerodrilus. The reduction of 

 the last pair of the three in Microscolex and Photodrilus brings about the condition which 

 characterises Ocnerodrilus. As compared with these forms, therefore, Ocnerodrilus occu- 

 pies a lower position, which I am inclined to attribute to degeneration. The dorsal vessel 

 is simple ; and there is a supra-intestinal trunk (fig. 3, s.n.). 



§ Nephridia. 



Dr Eisen found that in Ocnerodrilus occidentals " the segmental organs are present 

 in all setigerous segments except in the 13th and 16th. In the former they are replaced 

 by the oviducts, and in the latter by the efferent ducts and receptacle." 



This is not the case with my species. 



In a mature individual with the clitellum fully developed, which was studied by 

 means of longitudinal sections, the nephridia were clearly visible in all the segments of 

 the body, commencing with the Illrd, excepting only the Xlth and Xllth. 



The shape and structure of certain of the anterior nephridia agrees perfectly with 

 Eisen's description and figures ; and I can fully bear out, from my own observations, his 

 comparison with the nephridia of the Tubificidse. The appearance of the nephridia is quite 

 unlike that of any earthicorm, owing to the entire absence of blood-capillaries. This 

 point is not specially remarked upon by Eisen, though he figures no capillaries. This is 

 the first instance of an Oligochset having, as I shall point out later, marked affinities with a 

 particular family of Earthworms in which the nephridia are not furnished with a plexus of 

 vascular capillaries. Correlated with the absence of blood-vessels is the very small 

 development of the peritoneal layer surrounding the organs. Eisen does not indicate in 

 his figure any trace of such a structure at all, and I cannot say that I have been more 

 successful in detecting its presence in the nephridia of the anterior segments. 



I understand from Eisen's description that the nephridia of Ocnerodrilus occidentalis 

 present the same characters throughout the whole body, and he particularly remarks upon 

 " the absence of large translucent cells like those found in Rhynchelmis." I have also 

 already stated that this applies to the anterior nephridia of Ocnerodrilus Eiseni; but 

 from segment XX onwards the nephridia are seen to be partly embedded in a huge mass 

 of clear cells. A section through a nephridium of this segment is illustrated in fig. 9. 

 At the bottom of the figure are seen some of the coils of the tubules. These are surmounted 

 by a mass of cells, and a little to the left is another mass of similar cells, which in the 

 section selected for illustration appears to have no connection with the mass. This, 

 however, is merely due to the fact that the particular section does not show the con- 

 nection. The mass of cells in which the nephridium is partly embedded consists of 



