810 



ON THE CH^.TOSOMATID^ , 



the anterior extremity. They are comparatively short, 0-015 

 mm., and do not extend over the anterior margin of the rostrum. 

 There are no hairs or setpe on the posterior portion of the 

 rostrum, but several rows of hairs lying ventrad of the dorsal 

 seta?, which are almost as stout and as long as the setae, are on 

 a level with them, and are arranged in an exactly similar way. 

 The hairs on the trunk are fine and short, not more than 0-007 

 mm. long, and are quite inconspicuous. 



The lateral grooves on the rostrum (l.o.) are in the shape of a 

 strongly curved spiral, with the opening turned towards the 

 dorsal seta\ 



The anus is a transverse slit, 0*140 mm. from the tip of the 

 tail (Text-fig. 59, a). It is surrounded by an oval, flattened patch 

 of cuticle, which is finely pitted. Just behind it, two stout hairs 

 are inserted, and bend over towards it. 



Fig. 59. — X. cryptocephalum, 6 . 

 Posterior end; the penial set?e are seen througli the body- wall; ( x 480). 



The shape of the tail is peculiar. It is 0-066 mm. long, slender, 

 and sharply pointed. The cuticle covering it is finely pitted for 

 two-thirds of the distance to the tip, and, on the ventral side, it 

 is raised into six sharp ridges or serrations, which give it the 

 appearance of a saw (Text-fig. 59, ^/.). About midway along its 

 ventral surface, there are two hairs inserted close together. 



The cuticle is so thick that it is almost impossible to make out 

 any deta^ils of the internal structure. 



The alimentary canal (Plate 1., r^., i/^/.) is a tube continuous 



