i] STRUCTURAL AND SYSTEMATIC 7 



On segment xiv are a pair of very minute pores 

 a little in front of the ventralmost setae and thus 

 very near together. These are the openings of the 

 oviducts. Finally, near to the anterior border-line 

 of segments viii and ix and on a line with the 

 ventral pair of setae is a pore on each side through 

 which the cavity of the spermathecae reaches the 

 exterior. 



So much then for the external characters of our 

 worm. We next turn to the internal anatomy. When 

 the worm is opened by a longitudinal section from 

 end to end, and the two flaps of skin are turned 

 outwards and pinned down, the internal structure is 

 almost completely revealed. Running from end to 

 end is seen the alimentary canal ; the general cavity 

 of the body (coelom) in which it lies, as do of course 

 the other organs to be enumerated, is seen to be 

 divided by cross divisions, the intersegmental septa, 

 into a series of chambers which correspond with the 

 external division into segments. The septa are in 

 fact inserted on to the body-wall along the furrows 

 which mark the divisions between adjacent segments. 

 Anteriorly the large pharynx is responsible for con- 

 fusing the arrangement of the septa, which become 

 subdivided and fused or are prolonged a greater way 

 backwards and thus present a less obviously segmental 

 disposition. Certain of the more anteriorly placed of 

 these septa are much thicker than the rest. This is 



