.">74 MR FRANK E. BEDDARD ON THE ANATOMY OF OCNERODRILUS. 



It will be noticed from the above list that it is almost entirely among Earthworms 

 that we meet with this tendency for the vasa deferentia to become separate from the 

 atria.* If it were not for the striking instance to the contrary afforded by the Eudrilidae, 

 this point alone would be sufficient to justify the reference of Ocnerodrilus to Earth- 

 worms. As it is, the relationship of the vasa deferentia to the oviducts is an important 

 point of difference from all the Lumbriculiclse. 



In Dr Eisen's figure [1, pi. i. fig. 9, r, s] the atria are represented as passing back as 

 far as the XXVIth segment in a slightly undulating course, which is more marked 

 towards their caecal extremity. I have found that in my species the atria may also be, 

 but are not always, directed posteriorly from their point of opening on the XVIIth 

 segment. It is this position of the atria which gives them so unusual an appearance in 

 Eisen's figures, and perhaps led him to regard them at first not as atria but as spermathecse. 

 As a matter of fact, very little importance can be attached to the position occupied by 

 these organs in Oligochseta, where they extend through more than one segment. As a 

 general rule, they are more or less coiled up, and are limited to two or three segments in 

 the neighbourhood of that which bears their external orifice. But even in Acanthodrilus, 

 where this has been, according to my experience, always the case, there is one species, 

 viz., Acanthodrilus spegazzinii, in which the four atria extend back through a large 



* I assume that the structures which have been usually termed " prostates " in the Earthworm correspond to the 

 atria of the aquatic genera. This question has been lately revived by Benham, who is not of my opinion [10]. 



Before pointing out the reasons which lead me to adhere to my own view, I would say a few words concerning an 

 apparent confusion in my description which is pointed out by Benham. He says : " Beddard takes up rather a 

 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 ' Cementdriise ' (or prostate) of Tubifex. Now this prostate in 

 Tubifex has been shown by Vejdovskt 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 body cavity. The atrial 

 epithelium is derived from the epidermis, so that the ' Cementdriise ' is epiblastic, whereas the glandular covering of 

 the 'atrium' of Moniligaster, Stylaria, Rhynchelmis, &c, is mesoblastic, — if it is in reality a modification of peritoneal 

 cells. Hence Beddard would regard the epiblastic ' prostate ' (Cementdriise) of Tubifex as the homologue of the meso- 

 blastic covering of the atrium of Moniligaster ! ! " 



In my own Memoir, to which Benham refers [23], I compare (on p. 120) the glandular investment of the atrium 

 of Moniligaster with a corresponding investment of the atrium in Rhynchelmis, which I write down as " prostate," 

 indicating by the inverted commas that I follow the nomenclature of Vejdovsky. Further on I again (on p. 126) 

 make use of the term prostate in describing this glandular investment, but have omitted the inverted commas, which 

 renders my terminology a little confusing. I do not, however, in that paper compare the glandular investment of the 

 atrium in Moniligaster and Rhynchelmis with the Cementdriisen of Tubifex. 



In a preliminary notice of these facts, however [22], I did make this comparison, which appeared to me to be to 

 some extent justified by the remarkable fact that the Cementdriisen of Tubifex are not covered by a peritoneal coating. 

 I came to the conclusion later that the apparent discrepancy between Vejdovsky's statements and figures might be of 

 less importance than I had thought it. 



As to the terminal glandular structures attached to the vasa deferentia of Eudrilidae, Perichoetidse, Acanthodrilidse, 

 &c, it appears to me impossible to refer them to more than one category. 



Mr Benham indicates very clearly (except in fig. 4) the different layers which constitute these organs in a number 

 of types, but omits any representation of the family Eudrilidae ; it is precisely here that we meet with conditions which 

 render it impossible to distinguish between "atrium" and "prostate." Mr Benham allows " that a portion of the 

 prostate of Perichaita, Eudrilus, and other genera in which the sperm duct and the prostate join, is probably the homo- 

 logue of the 'atrium' of Tubifex. : ' To follow out this admission to its logical conclusion it is necessary to draw a 

 distinction between the part immediately preceding and the part immediately succeeding the point of opening of the 

 ■• i i 'I' f'-n ntia ; thai i- to ay, we tnu i regard as differenl two parte of a tube in tin' Eudrilidae and in the Lumbri- 

 enlidse between which there is no trace of a break, and not the faintest difference in minute structure ! ! 



