264 • FRANK Tl. BEDDARD. 



the atrium into a glandular and an efferent section, such as 

 is found in Hyperiodrilus and in other earthworms. There 

 is no such sharp demarcation between the highly glandular 

 more distal part of the atrium and the duct which perforates 

 the body-wall, and is lined with simple columnar epithelium. 



The glandular part of the atrium has the typical structure, 

 although the demarcation between the two layers of cells was 

 obscured by the great abundance of secretion; the inner layer 

 conld be only detected by the presence of a regular row of 

 nuclei. Towards the external aperture the character of the 

 lining epithelium gradually alters : this alteration affects, in 

 the first place, the thickness of layers ; they become gradually 

 thinner, until not far from the external orifice there is but a 

 single layer of cells. The cells in this layer (fig, 39) are of 

 two kinds — large swollen glandular cells with a scanty amount 

 of protoplasm lie embedded in a mass of narrow columnar cells ; 

 when the tube enters the body-wall on its way to the exterior 

 the glandular cells disappear, and there are only columnar cells 

 present of a non-glandular character. 



The vasa deferentia, as in Hyperiodrilus and 

 Eudrilus, open into the glandular portion of the atrium, 

 which is, I should remark, not divided into two chambers 

 bound up in a common sheath, as it is in Eudrilus. The 

 two vasa deferentia retain their distinctness, and open into 

 the atrium (fig. 42) at some little distance from each other. 



The glandular part of the atrium has a very thin muscular 

 sheath ; this becomes thicker towards the external orifice, 

 where it is plainly divisible into two layers — an outer layer of 

 circular fibres, and an inner layer of longitudinally running 

 fibres. The layers, however, are even here very thin, and do 

 not consist of more than two rows of fibres. The two atria 

 traverse the body-wall independently of each other, and unite 

 at the bottom of a tubular depression which communicates 

 directly with the exterior. The structure of the parts is such 

 that it does not appear to be capable of eversion as a penis. 

 There are no penial setse present. The body-wall is consider- 

 ably thickened in the region of the atria for some distance on 



