:6 



compressorium the labrum gets pushed forward and takes a horizontal 

 position, so that all the parts can easily be seen, and it is in this 

 somewhat unnatural position that it is shown in my figures of the head. 



For convenience of description we may divide the labrum into 

 three portions, (i) the dorsal surface, (2) the anterior free extremity or 

 "lip," and (3) the ventral surface or " epipharynx." The dorsal 

 surface is chiefly made up of two sclerites or thickenings of the cuticle. 

 The posterior sclerite is an elliptical chitinous plate abutting on the 

 anterior edge of the clypeus ; from its foci arise long chitinous hairs. 

 In some species this plate is absent, e.g., in No. 13 ; in others it is fused 

 to the clypeus ; and in one species (No. 15) it is found in a partially 

 evolved condition. 



In figure 6 we can clearly see that the complete sclerite must 

 have arisen from the growth of two separate sclerites forming around 

 the chitinous hairs, and which, gradually approaching each other, finally 

 coalesced into a single plate. 



The anterior sclerite is much larger and of more complex outline ; 

 in front it extends right across the labrum, and curving round the 

 sides is seen to give attachment to appendages on the ventral surface, 

 while behind it narrows and, after giving rise to " lateral inlets," extends 

 backwards until close to the posterior sclerite. Near each inlet a 

 chitinous hair is found ; these may be the starting points of separate 

 sclerites which afterwards fused together, but we have no proof in this 

 case. In the clear space on each side of the anterior sclerite is a long 

 chitinous hair with two short hairs arising from the same base, i.e. a 

 triple chitinous hair, surrounded by an exceptionally large chitinous 

 ring, the largest in the body. 



The Lip. The lip is non-chitinous and bears a number of sensory organs. 



At the base are a pair of median short hairs, and outside them a pair 

 of broad-based prominences bearing minute papillae. Above these and 

 somewhat more central is another pair of prominences, stalk-like and 

 bearing on their free ends long toothed feelers. At the anterior 

 extremity of the lip, from a kidney-shaped bulb, arise a pair of 



