312 W. BLAXLAND BENHAM. 



Eudrilus (see Beddard, 2, pi. xxxiii, fig. 17; and Horst, 

 22, figs. 3, 4). 



Some of these deserve further mention. 

 In Criodrilus the narrow tube is very much more extensive, 

 and undergoes a greater amount of coiling than in Lum- 

 bricus, and herein rather agrees with the Microdrili. There is 

 no muscular duct, the wide tube penetrating the body-wall as 

 far as the circular muscles (PI. XXIV, fig. 17). It is sur- 

 rounded by a very loose connective tissue as it passes through 

 the longitudinal muscles ; and this connective tissue is modified 

 just before the tube reaches the circular muscles. Here can be 

 seen seven or eight, or perhaps a few more, nuclei belonging to 

 certain cells, which are elongated transversely to the long axis 

 of the tube (fig. 17, y) ; they resemble, in position and arrange- 

 ment, the '' sphincter muscle-cells " figured by Spencer around 

 the tube of the large nephridia of Megascolides; but in 

 Criodrilus they are certainly not muscle-cells. 



At this point, when the tube has reached the circular 

 muscles, it becomes difiicult to be sure of the exact nature of 

 the wall — i. e. whether it is formed by perforation of cells 

 or by an epithelium ; for the nephridial tube undergoes a slight 

 flexure here, in order to reach the deep but narrow pit formed 

 by invaginated epidermis, and constituting the nephridiopore. 

 A study of several series of consecutive sections through this 

 region, however, gives me the impression that there is a very 

 short intercellular tube between the wide tube and the epi- 

 dermic pit : this then would correspond to the duct or muscular 

 region of Lumbricus deprived of muscle-cells, the contrac- 

 tion of this part being, when necessary, brought about by the 

 muscles of the body-wall. This anatomical difference between 

 Lumbricus and Criodrilus seemed, when I first observed it, 

 to agree with the different descriptions of the development of the 

 nephridia given by various authors ; some aflBrraing the exist- 

 ence of an epiblastic invagination to meet the mesoblastic tube, 

 others denying this invagination, e. g. Bergh in Criodrilus 

 (12), where, indeed, we should not expect it to occur ; but 

 Bergh has quite recently (13) emphatically denied it also 



