STEUCTUEE OP EAETHWOEM OF GENUS DIACH^TA. 171 



It is clear from the above very brief account of the organi- 

 zation of Diachseta that, as Mr. Beuham pointed out, it is 

 closely allied to Urochseta, 



But the two species of Diachseta differ from each other in 

 most of their points of agreement with Urochseta. In both 

 species there is no prostomium, and the setae alternate in posi- 

 tion from segment to segment as they do in Urochseta, though 

 the alternation begins from the very first in Diachseta, and 

 not until later in Urochseta; there are five strong septa 

 commencing behind Segment vi, and three pairs of simple 

 spermathecse. Diachaeta Thomasii agrees with Urochseta 

 in having only a single pair of testes, sperm-sacs, and 

 vasa deferentia. 



Diachseta Windlei, as I desire to name my species, 

 agrees with Urochseta in that the clitellum commences at 

 Segment xv, and in the mass of muscles which surrounds the 

 aperture of the nephridia. 



In the following table the principal points of resemblance 

 and difference between the three forms are shown : — 



