468 Illinois State Laboratory of Natural History. 



tains but few or none, and the walls of the two regions are 

 decidedly different in structure except in the parts adjacent. 



The spermathecal wall consists of outer and inner epithelial 

 layers, in addition to. which layers of muscle tissue are 

 present in the duct. The outer epithelium is everywhere 

 thin, and composed of flattened cells except near the middle 

 of the duct, where this layer is considerably thickened and 

 the cells are columnar in character. The inner epithelial 

 layer is of moderate thickness in the duct and in the greater 

 part of the storage region, and its cells stain quite deeply in 

 hematoxylin. In the remainder of the storage region and in 

 the glandular part this layer becomes quite thick, and is 

 composed of columnar cells having their nuclei in the basal 

 portion and staining only slightly in Ehrlich's hematoxylin. 

 A layer of circular muscle fibers, which lies next to the inner 

 epithelial layer and is comparatively thin, is present through- 

 out the whole length of the duct. Between this layer and the 

 outer epithelium there is a layer of longitudinal muscle fibers 

 which is quite thick in the greater part of the duct, but thins 

 out, and finally disappears in the part nearest the storage 

 region. 



From the foregoing description it is evident that Premno- 

 drilus palustris belongs to that branch of the Lumbriculidce 

 which includes the peculiar genera Eclipidrilus and Meso- 

 porodrilus. For the purpose of studying the relationships of 

 these different forms, a more extended examination of the 

 nephridia! and circulatory systems of Mesoporodrilus asym- 

 metricus has been made, the results of which are next 

 recorded. 



Nephridial and Circulatory Systems of Mesoporodrilus asym- 



metricus Smith. 



In the original description of this species the only reference 

 to the nephridia is to the effect that the first pair is in VII, 

 and that the nephridiopores are in front of the ventral seta' 

 (Smith '96, p. 404). A re-examination of the material studied, 

 however, with more careful attention to the nephridia, shows 

 that the main masses of the pair belonging to VII extend 



