MR FRANK E. BEDDARD ON THE ANATOMY OF OCNERODRILUS. 



573 



Atria. 



These organs were noted by Eisen in his original paper upon Ocnerodrilus, but 

 regarded, on account of their opening on to the exterior independently of the vasa 

 deferentia, as spermathecse. 



Vejdovsky [15, p. 149], in a woodcut illustrating the male ducts of the Annelid, 

 figures this supposed spermatheca as an atrium. 



That this interpretation, which I have myself already accepted, is correct, I am 

 able to prove in the present paper. Eisen himself has lately admitted the justice of 

 Vejdovsky's correction of his statement [15]. He says in a footnote to p. 5 : " The organs 

 which I have there described as seminal receptacles are undoubtedly nothing but the 

 atrium. During a recent visit to Central America I found four new species of Ocnero- 

 drilus, and a cursory microscopic investigation showed me immediately that the seminal 

 receptacles existed in several pairs in some of the anterior segments, which makes it 

 evident that the large bodies which open in the same porus as the efferent ducts must 

 be considered as atrium. In the Californian species, which I described as 0. occiden- 

 talis, these small seminal receptacles were evidently overlooked." I refer to the last- 

 mentioned point on p. 14. As to the atria, I find in my species that they do not open 

 on to the exterior independently of the vasa deferentia. It is very possible that the 

 study of the living worm as a transparent object might lead to this conclusion, since the 

 vasa deferentia only communicate with the atria just before the latter open on to the 

 ventral surface of the body. On the other hand, it is equally possible that both Eisen 

 and myself are right, and that there is actually this difference between the two species, 

 which are nevertheless in other respects closely allied. The degree of connection 

 between the vasa deferentia and the atria in the Oligochseta presents a most interesting 

 series of modifications between absolute independence at one extreme and perfect con- 

 tinuity at the other. 



The following Table indicates the several stages, so far as they are known at 

 present : — 



I. Atria presenting the appearance of a simple ter- 

 minal dilatation of the vas deferens (or vasa 

 deferentia) — 

 Chcetogaster, Tubifex, Psammoryctes, &c. 



II. Vasa deferentia opening into the atrium at the 

 side — - 

 Lumbriculidce,* Eudrilidce, Moniligader* 



III. Vasa deferentia opening into the atrium at the 

 commencement of the non-glandular por- 

 tion — 



Perichceta, Pontodrilus, &c. 



IV. Vasa deferentia opening into the atrium just 

 before its opening on to the exterior — 



Ocnerodrilus Eiseni. 



V. Vasa deferentia opening independently of and 

 just behind the atrium — 



Typhwus, Rhododrilus. 



VI. Vasa deferentia opening independently of the 

 atrium in the next segment — 



Neodrilus, Acanthodrilus. 



* In these Oligochseta there is hardly any distinction between a glandular and non-glandular section of the atrium. 



