some neto Species t)/ Drawkla. 509 



secondary mesenterial tube. Each duct turns inwards and 

 pierces the very thin septum 9/10, and runs below the parietal 

 lobes of the nepliridium and joins tlie spermiducal gland on 

 its upper anterior margin, just at the point where the 

 second seminal duct enters it. The latter is a shorter and 

 thicker non-convolute tube. In microscopical structure 

 they resemble one another, except for the fact that in the 

 shorter duct belonging to somite 10 there is an envelope of 

 circular muscle-fibres outside the cubical epithelium, which 

 is, howevei-, ciliated in the longer duct belonging to the 

 anterior somite. In the funnel of the anterior sperm-duct, 

 the cells are more columnar and also ciliate. The cytoplasm 

 stains deeply, and the nucleus is large and centrally placed in 

 the funnel-cells. There is a distinct, though very thin, 

 peritoneal outer layer for the posterior sperm-duct, which is 

 simply an upward extension of the outer layer of the spermi- 

 ducal gland. 



The prostate or spermiducal gland (PI. XVIII. fig. 10^') is 

 a comparatively small structure, spherical and yellowish, and 

 the greater p;irt of the atrium is buriedin the body-wall. It 

 has two sources of blood-supply, both from the subintestinal 

 and lateral longitudinal vessels, and small branches extend on 

 to the sperm-vesicles. There are the usual two kinds of club- 

 shaped glandular cells, the large and small ones, iu addition 

 to the more spherical, also glandular, cells. The circular 

 muscles are confined to the duct-like prolongations of the 

 gland-cells. There is a peritoneal investment, and groups 

 of cells are found near the necks of the glandular larger cells, 

 and the diSerences between these fourth group of cells and 

 the glandular cells in their contents are more clear, stain less 

 easily, and the spherical small nucleus is very clear in them. 

 The cubical epithelium of the atrium is more or less horny 

 on its inner surface. The outer lips of the male atrial 

 orifice are swollen and comprise a mass of smaller oval 

 glandular cells, which occur in great uniformity over the 

 whole clitellum and the copulatory brackets themselves, 

 which are several layers deep. In addition to these smaller 

 cells, there occur in equal abundance the more common 

 flask-shaped cells. Almost as a rule, whatever may be the 

 shape and size of these gland-cells the nucleus is pushed to 

 one side of the cell-body, and this position of the nucleus 

 becomes so pronounced that it may be used for distin- 

 guishing the epithelial cells with granular cytoplasm, in which 

 the cells are more centrally situated. 



The occurrence of two pairs of sperm-vesicles in D. soma- 

 varpatna is not without significance in this genus, although 



