270 FRANK E. BEDDAED. 



primitive or non-primitive condition of the reproductive system 

 in Eudrilus. 



The atria present the appearance of the corresponding 

 organs in Acanthodrilus or Pontodrilus — that is to say, 

 they form two somewhat bent tubes of an opaque white 

 colour; they differ, however, in the fact that it is impossible 

 to distinguish a muscular and a glandular portion : in the two 

 genera mentioned, and in many other forms in which the atria 

 are tubular, the organ communicates with the exterior by a 

 narrow duct ; this duct is lined with an epithelium -which is 

 not in the least glandular, and is surrounded by a tolerably 

 thick muscular coat. In Nemertodrilus no such duct is 

 present; the organ is identical in structure throughout with 

 the glandular part in Acanthodrilus: its epithelium is of 

 two kinds ; the innermost layer is formed by a single row of 

 unusually short columnar cells ; beneath these are the usual 

 layers of pyriform gland-cells, each wdth a long slender pro- 

 longation which reaches, or nearly reaches, the lumen of the 

 gland. 



As Perrier (8) first remarked, the atrium of Eudrilus is 

 remarkable on account of its nacreous appearance and per- 

 fectly straight course. The nacreous appearance is due to an 

 enormouslj'^ thick muscular coat, which I figured in transverse 

 section in a paper dealing with the structure of Eudrilus 

 sylvicola (1). 



In Nemertodrilus, as I have already implied by compar- 

 ing the appearance of the organs to that presented by the 

 atria of Acanthodrilus and Pontodrilus, the nacreous 

 appearance is entirely wanting. Sections of the atrium, 

 however, show that the muscular coat itself is not absent, 

 but is greatly reduced as compared with Eudrilus and, ac- 

 cording to Rosa's observations, Teleudrilus. The whole 

 organ, in fact, is a little more degenerate than that of Eu- 

 drilus. Considering the absence of the duct, which is 

 so universal a feature of the atrium among earthworms, I 

 should be disposed to regard the atrium of Nemertodrilus 

 as having been derived from that of Eudrilus by reduction. 



