STRUCTURE OF A GENUS OF OLIGOCH^ETA. 7 



To return to the apparent difference in position of the testes and vasa deferentia : 

 it looks almost as if in fig. 8 the testes and vasa deferentia funnels were attached to the 

 posterior wall of segment IX ; on the other hand, in fig. 9, the position seems to be 

 different ; the testes seem to be attached to the anterior wall of segment X, and the vas 

 deferens funnel to be attached to the same septum, without perforating it so as to lie in 

 segment IX. Fig. 8 is from a series of sections taken through Xth and neighbouring 

 somites, and it seems to agree with another series taken from the whole of the anterior 

 part of the body, which, however, were not in a very good state of preservation. 



I do not see how it is possible to reconcile these two sketches on the hypothesis that 

 the vas deferens funnel and testes have an identical position ; it must, I think, be admitted 

 that in two out of the three specimens the funnel lies in segment IX, and that the testes 

 are attached to the posterior wall of this segment, while in the third specimen the 

 funnel and testis are in segment X. 



This difference appears to coincide with a difference in the position of the gizzards, and 

 possibly means that I am dealing with two distinct species. 



I do not see how any distortion produced by growth or even by action of reagents can 

 alter the position of the testes to so great an extent as is indicated in the two figures 

 (figs. 8, 9) ; in one case the base of the testis is directed posteriorly, in the other case 

 anteriorly. 



Vas Deferens. — There are a single pair of these ducts which open into the atrium ; 

 the funnel lies either in the same segment as that which carries the external aperture, or 

 in the one in front (IXth) ; I have already remarked, in describing the testis, that this is 

 probably a specific difference. 



The most important point to be noted about the funnel is the extreme simplicity of 

 its structure ; instead of being folded and plaited, as in earthworms generally, it is, as in 

 the Limicolse, a comparatively simple disc, hardly standing out from the surface of the 

 intersegmental septum to which it is attached. 



Atrium. — As I have already fully described the atrium with a figure [4], I need do 

 no more here than mention the fact that the atrium as described by me, was that of the 

 individual in which the funnel appeared to be in the IXth segment ; it is so far additional 

 evidence in favour of the differences in the position of the funnel being specific differences, 

 that the specimen in which the funnel appeared to be in the Xth segment, had an atrium 

 somewhat different in structure. The groups of glandular cells surrounding the atrium 

 are no longer distinguishable; the lining epithelium is surrounded by a thick mass of 

 tissue, which is partly formed of cells and partly of muscular fibres, but there is no differen- 

 tiation into a distinct muscular layer surrounded by a glandular layer. On the whole, it 

 appears to me to be more probable that the atrium is in an immature condition, and that 

 the glandular and muscular layers are not yet differentiated out of the peritoneal invest- 

 ment of the epidermic invagination (in which way I suppose that the atrium originates). 

 The atrium in this instance is in fact rather to-be compared with the immature sper- 

 matheca described and figured by Bekgh [7, p. 328, pi. xxi. figs. 23, 24]; and it seems 



