300 W. BLxVXLAND BENHAM. 



Fig. 2. — The complete nepbridium as seen (for the most 

 part) in optical section^ without any blood-vessels. It shows 

 the character of the tubule in the different regions (note espe- 

 cially the ciliated tracts), the course of the tubule, and the 

 arrangement of the constrictions, so as to form loops. C. 

 The ampulla. 



E. The muscular duct in the first " loop." F F. The second 

 "loop." G G. The third '^oop." /. The pr^septal region, 

 with the nephrostome. a, b, c, d, e, f, g, h point to difierent 

 parts of the " narrow tube." O. The muscular duct, dipping 

 into body-wall to open externally. 



a — b. The first ciliated tract of the '' narrow tube." c — c' 

 (at the apex of the second " loop ") is the second ciliated tract 

 of the narrow tube, d — e is the narrow tube in the third 

 ^'\oo^.'' e — e. The third ciliated tract in the recurrent part 

 of the narrow tube, /to g, to h. The remainder of the recur- 

 rent part of the narrow tube lying in second ^' loop." 

 h—j. The ciliated " middle '' tube in the third " loop." 

 k — I. Part of the '' wide" tube in the third ''loop." / — m. 

 The " wide" tube in the second " loop." m — n. The " wide " 

 tube in the third " loop." n points to the junction of the wide 

 tube with the muscular duct, where the tube is no longer seen 

 in section, but in surface view. r. Nucleus of one of the cells 

 covering muscular duct. s. A muscle-fibre, part of the net- 

 work on the muscular duct, t t. Vesicular connective tissue, 

 in which the tubule is embedded for the greater part of its 

 course. 



