OCR Text |
Show 1893.] PROSTATE IN THE OLIGOCH.ETA. 477 genus Moniligaster " the prostates are formed by a metamorphosis of certain peritoneal cells." The real equivalent therefore of the " prostates " in the Limicolae and in Moniligaster are to be found in the peritoneum of Acanthodrilus, Perichceta, &c. " In Earthworms therefore," I concluded, " there are two organs which have been termed prostates-(1) the atrium of Acanthodrilus, Perichceta, &c.; (2) the atrium + prostate of Moniligaster." These opinions were upheld with slight modifications in a subsequent paper (5, p. 117 &c). One important difference between the atria of the higher and those of the lowTer Oligochaeta 1 sought to explain by the primitive position of the atrial pores. Assuming that they originally were developed as invaginations of the clitellar region, it would follow that the lining membrane would consist, as does the clitellum, of two layers of cells; the resemblance of the cellular lining of the atrium in Acanthodrilus &c. to the clitellar epithelium has been commented upon by others as well as by myself. In the lower Oligochaeta, on the other hand, the clitellar epithelium is one-layered; hence the lining membrane of tbe atrium is one-layered also. M y later discovery, made since the paper to which I am now referring was written, that Moniligaster has a clitellum like that of the low7er Oligochaeta, still further confirms this way of looking at the facts. In the lower Oligochaeta the atrial epithelium is ciliated-another difference as I then thought it; I have, however, lately found that in Eudriloides brunneus (n. sp.) the same ciliation at any rate partially occurs. I need not therefore recapitulate my attempt to explain what is now not a difference between the lower and higher genera of Oligochaeta. Other points in this paper will be referred to again. The views expressed in m y papers were controverted by Benham (10). He points out in the first place a confusion of terms of which I was guilty. Mr. Benham writes :-"Beddard takes up a rather curious position in regard to the prostate of Moniligaster. For him the peritoneal coat, outside the muscular wall of the atrium, is the ' prostate' and is homologous with the " Cement- Driise" (or prostate) of Tubifex. N o w this prostate in Tubifex has been shown by Vejdovsky to be formed by a proliferation and outgrowth of the atrial epithelium at a certain point, which bursts through the muscular wall of the atrium and projects into the bod} -cavity. The atrial epithelium is derived from the epidermis, so that the ' Cement-Driise ' is epiblastic ; whereas the glandular covering of the ' atrium' of Moniligaster, Stylaria, Bhynchelmis, &c. is raesoblastic,-it is in reality a modification of the peritoneal cells. Hence Beddard would regard the epiblastic ' prostate' (Cement-Driise) of Tubifex as the homologue of the mesoblastic covering of the atrium in Moniligaster! " I did make this comparison at first; and it seemed to me to be justified by the curious fact that in Tubifex the Cement-Driise was not covered by peritoneum, the rest of the atrium being covered; the disappearance of the peritoneum at this particular point appeared to m e to indicate that possibly the data of Vejdovsky were not perfectly accurate. |