STRUCTURE OF A GENUS OF OLIGOCH^ETA . 15 



POSTSCRIPT ADDED JUNE 2, 1890. 



Since the foregoing was written, I have received an important paper from Dr Rosa* 

 dealing partly with the anatomy of the Moniligastridse. 



As I have already pointed out, Dr Rosa was inclined to doubt in some particulars 

 the accuracy of my description of the reproductive organs of Moniligaster. He now 

 describes a species, which he has done me the honour to dedicate to myself, which agrees 

 very closely in structure with M. Barwelli. 



It is gratifying to me to read this description ; the doubts which were thrown upon 

 my work by so able an investigator of the group as Dr Rosa has proved himself to be, 

 caused me some anxiety. 



In Moniligaster Beddardii the position as well as the structure of the genitalia appears 

 to be precisely as in M. Barwelli. Dr Rosa describes the funnel of the vas deferens as 

 being flattened out, and not projecting much into the interior of the sperm sac ; the 

 testes also are attached to the funnel itself. The figures published in the present paper 

 are quite in accord with those of Rosa. I have ventured (vide supra) to suggest that 

 the ovary is in all probability contained in the Xlth segment ; I also identified a ciliated 

 funnel-like structure attached to the hinder wall of this segment as the oviducal funnel 

 These identifications are rendered practically certain by Rosa's very clear diagram of the 

 genitalia of M. Beddardii. A second interesting species is referred to a distinct genus 

 — Desmogaster. Desmogaster Dorics has two pairs of atria opening on to the interseg- 

 mental grooves XII/XIII and XIII/XIV, all four apertures being distinct ; as in Monili- 

 gaster, the vasa deferentia open into the atrium; the vasa deferentia, funnels, testes, and 

 sperm sacs are as in Moniligaster, though, of course, four in number. The structure of 

 the atria is rather different ; there is the same central epithelium and annular layer of 

 muscles ; outside this are the groups of glandular cells that are met with in Moniligaster, 

 but they are interspersed with muscular fibres ; there appears to be also a delicate peri- 

 toneal investment. Dr Rosa considers that the resemblances of the atrium here are rather 

 with other earthworms, though possibly the organ is to be regarded as intermediate in 

 character, connecting such a form as Eudrilus with Moniligaster. 



The glandular cells are regarded as being referable to the lining epithelium, but a 

 complete circular layer of muscular fibres is figured between them and the single layered 

 epithelium. It seems to me to be still possible to refer all which lies outside of the 

 lining epithelium to the peritoneum. Unfortunately, in this, as in so many other ques- 

 tions concerning the morphology of the Oligochseta, there is no assistance to be got from 

 embryology. The development of the spermathecse, however, offers an analogous case, 

 which supports the view that all the structures lying outside of the lining epithelium are 



* Viaggio di Leonardo Fea in Birmania e regioni vicine xxv. Moniligastridi, &c, Ann. Mus. Civ. Geneva, vol. ix., 

 1890, p. 368 et seq. 



VOL. XXXVI. PART I. (NO. 1). D 



