20 Journal of the Asiatic Society of Bengal. [N.S., X1X, 
these in a few forms. According to Heymons the so-called labial 
palps are secondary structures formed from the 3rd segment of 
the proboscis, whilst Léon maintains that it is not possible for 
argument of Léon does not appear to be convincing, since it 
is highly probable that these secondary structures of Heymons 
are not sensory and do not perform the function of the original 
palps ; the sensory activity of the labium having been trans- 
ferred to the tip of the rostrum. 
Morphology of the mouth parts : Labrum (LR. Figs. 3b, 4b, 
7b), is an unpaired flap hinged to the anterior margin of the cly- 
peus. It is tapering towards its free end and 2 mm. long, extend- 
ing as far as the first segment of labium. It has a broad base 
and semilobate margin. . The dorsal surface is covered with 
smal] (sensory) hairs or epedind On the ventral surface runs 
h 
deep to hold the stylets in place and to prevent their lateral 
movements, 
Rostrum or labium (LB. Figs. 6a, 3b) is the segmented 
lower lip. It is sub-cylindrical in cross section, with a longi- 
tudinal groove running down its dorsal surface. In the region 
of the Ist segment the groove is very shallow as mentioned 
above, but beyond the apex of the labrum it deepens and 
forms a trough in which the stylets lie (Fig. 6c). Two tra- 
cheae, two nerve cords and several muscle bands run through- 
out its length (Fig. 6c). Of the four segments constituting the 
labium the first is broader and shorter, the joint between 
this and the next is swollen and acts as a hinge upon which 
the whole of the Jabium is bent and doubled when the animal 
is sucking plant juice. This bending and shortening of the 
proboscis facilitates mechanically the penetration of the 
stylets in the deeper tissues of the plant. The 2nd, 3rd and 
4th segments are narrow and long, and the proboscis gradually 
tapers towards the extremity which is black and bifid. Kach 
lobe of the bifid tip bears six small papillae as well as four 
long curved pointed bristles (Tig. 61). 
here are two pairs of stylets, internal (maxillary) and 
external (mandibular). The lateral edges of the clypeus to- 
inside the head pie 7b). On entering the head, the two pairs 
of stylets diverge apart (Fig. 6a), one member of each pair lying 
on each side of the pharynx, the mandibular (external) being 
more neat 
e base of the maxillary stylet is much swollen and, in 
transverse section (Mx. . Figs. 8a, b), presents the appearance 
of a glandular tissue surrounded by a thin layer of chitin. As 
the sections are traced forwards, the stylet becomes hollow and 
oh ae he? elnino. 



