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Show 1887.] ANATOMY OF EARTHWORMS. 383 well-developed muscular coat (fig. 11,6); the lining epithelium is ciliated throughout. The terminal apparatus of the male generative system in Eudrilus is extremely unlike what is found in other Earthworms. It has been already partly described by Perrier and by myself; but these descriptions refer only to the rough anatomy of the organs, and not to the minute structure. With regard to one point there is some discrepancy between Perrier's account and m y own, and that is the termination of the vasa deferentia. These tubes, as already stated, are remarkable for the fact that they possess a thick muscular coat, which is wanting in the vasa deferentia of other Earthworms; the two vasa deferentia, instead of uniting to form a single tube, as they do in the majority of Lumbricidae (in all except Acanthodrilus), remain distinct and open separately into the terminal region of the prostate gland. M. Perrier has figured (I. c. pl ii. fig. 26, a) a single vas deferens opening into the muscular sac of the penis in Eudrilus decipiens ; and there are no statements in his paper which would lead to the inference that in the two other species there was a difference in respect of these organs. Towards their distal extremity the vasa deferentia increase notably in diameter (cf. figs. 1, 16). In Eudrilus boyeri I found the important difference in the vasa deferentia and in their relation to the terminal apparatus that has been just referred to, and which is fully described aud figured in m y paper upon that species ; aud I am now in a position to state that in Eudrilus sylvicola the arrangement of these organs is precisely similar. This fact renders it probable, in m y opinion, that the structure of tbe terminal apparatus of the male sexual organs in Eudrilus generally is closely similar to that of E. sylvicola, which is now to be described in detail. On opening the body of the worm the conspicuous prostate glands are to be seen, which extend back from their opening into the bursa copulatrix of the 17th segment for some way. M. Perrier rightly points out the nacreous appearance of this organ, which only resembles the prostate gland of other Lumbricidae by its position : - " mais qui ne presente en aucune facon l'aspect glandulaire de ces dernieres." An investigation of the structure of this sausage-shaped body shows very plainly that it is of a glandular nature and that it resembles in many points the prostate glands of other Earthworms. The glandular nature of the organ is, however, masked by the very great development of its muscular layers, which give to it the peculiar nacreous appearance which is so characteristic. A study of the organ by means of transverse sections (see Plate XXXIII., fig. 13) shows that these muscular layers together form a coat of very considerable thickness ; by far the greater part is occupied by the longitudinal fibres, the transverse fibres forming a very delicate layer within these. The glandular tissue of the organ is divided into two layers, which agree very closely in structure with the prostate glands of Acanthodrilus, and also present an unmistakable resemblance to the epidermis of the clitellum. The inner row of cells which surround the lumen of the gland are narrow, elon- 26* |