I] STRUCTURAL AND SYSTEMATIC 21 



with fine ridges but are bifid at their free extremity. 

 The prostomium is often apparently completely 

 absent. It is however really present but is retractile. 

 As to the pores which are visible externally the 

 dorsal pores are completely absent. The pores of the 

 nephridia lie in front of the dorsal pair of setae or in 

 a line corresponding to the position of those setae 

 where the arrangement has become irregular. The 

 spermathecal pores are three pairs and are in the 

 very front of segments vii, viii, ix. The male 

 pores, very inconspicuous, lie on the ventral side of 

 segment xxi just within the clitellum. The oviducal 

 pores are on segment xiv. 



As to internal anatomy the general plan of the 

 segmentation shows no great diflferences. Certain 

 septa only show a diffference, i.e. those separating 

 segments vi-xi which are specially thickened. In 

 the alimentary canal a gizzard in segment vi is to be 

 noted and three pairs of calciferous glands in segments 

 vil-ix. The nephridia are paired structures and 

 commence early. The first two or three segments 

 are occupied by a pair of large glands opening into 

 the buccal cavity which are apparently a slightly 

 modified pair of nephridia and are generally termed 

 * peptonephridia ' since they are associated, as it 

 would appear, with the function of alimentation and 

 are not purely excretory organs. There is but a 

 single pair of spermaries in segment xi, and of 



