1893.] PBOSTATE i:S^ THE OLIGOCH.lSrA. 477 



genus MoniUgaster " the prostates are formed by a metamorphosis 

 of certain peritoneal cells." The real equivalent therefore of the 

 " prostates " in the Limicolfe and in MoniUgaster are to be found 

 in the peritoneiun of Acanthodriltis, Perichceta, &c. " In Earth- 

 worms therefore," I concluded, " there are two organs which have 

 been termed prostates — (1) the atrium of Acantliodrilus, Penchceta, 

 &c. ; (2) the atrium + prostate of MoniUgaster." 



These opinions were upheld with slight modifications in a subse- 

 quent paper (5, p. 117 &c.). One important difference between 

 the atria of the higher and those of the lower Oligochseta 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 i\\o layers of cells ; the resemblance of the 

 ceUular lining of the atrium in Acantliodrilus &c. to the clitellar 

 epithelium has been commented upon by others as well as by 

 myself. In the lower Oligochseta, on the other hand, the clitellar 

 epithelium is one-layered ; hence the lining membrane of the 

 atrium is one-layei-ed also. My later discovery, made since the 

 paper to which I am now referring was written, that MoniUgaster 

 has a clitellum like that of the lower Oligochseta, still further con- 

 firms this way of looking at the facts. In the lower Oligochajta 

 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 thei'efore 

 recapitulate my attempt to explain what is now not a difference 

 between the lower and higher genera of Oligochseta. Other points 

 in this paper will be referred to again. 



The views expressed in my papers \\ere 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 MoniUgaster. 

 Yov him the peritoneal coat, outside the muscular wall of the 

 atrium, is the 'prostate' and is homologous with the " Cement- 

 Driise" (or prostate) of Tuhifex. Now this prostate in Tuhifex 

 has been shown by Vejdovsky to be formed by a prohferation and 

 outgrowth of the atrial epithelium at a certain point, which bursts 

 through the muscular wall of the atrium and projects into the 

 bodj -cavity. The atrial epithelium is derived from the epidermis, 

 80 that the ' Cement-Driise ' is epiblastic ; whereas the glandular 

 covering of the ' atrium' oi MoniUgaster, Stglaria, liJigncJwIjnis, &.c. 

 ia raesoblastic, — it is in reality a modification of the peritoneal 

 cells. Hence Beddard would regard the epiblastic ' prostate ' 

 (Cement-Drli.se) of 2'uljife.v as the homologue of the mesoblastic 

 covering of the atrium in MoniUgaster ! " I did make this compa- 

 rison at first ; and it seemed to me to be justified by the curious 

 fact that in Tidnfex the Cement-Driise was not covered by j)eri- 

 toneum, the rest of the atrium being covered; the disap])earance 

 of the peritoneum at this particular point appeared to me to indicate 

 that possibly the data of Vejdovsky were not perfectly accurate'. 



