GENERAL INTRODUCTION. 9 



lying outside the true clypeus ; its apex may be acute or 

 rounded, and the sides may extend downwards to the base 

 of the true clypeus. The false clypeus is not present in the 

 earlier instars, but is always present in the last instar, though 

 sometimes it is difficult to trace, as in the genus Macroglossum. 



The labrum (fig. 2 A, e) is a transverse plate, the proximal 

 part chitinized, the distal part generally membranous ; 

 measured along the dorsal line it is between one -half to 

 one-third the length of the true clypeus. The front or lower 

 margin is straight and the hinder margin arched towards the 

 base of the clypeus ; the hinder margin is connected with 

 the base of the clypeus by membrane which allows it a certain 

 amount of movement. In many species the labrum is 

 sculptured by longitudinal ridges, as shown in the figure, 

 but in other species it is smooth ; at each side there is a 

 prominent bristle (fig. 2 B, e), which is directed forwards, 

 downwards and inwards. 



The ligula (figs. 2 A,/; 2 B, a) lies below the labrum, and 

 serves to direct the edge of the leaf to the cutting surfaces 

 of the mandibles when the larva is feeding. It is apparently 

 developed from the lining of the gullet, being rooted under 

 the labrum and independent of it, as is shown both by dis- 

 section and by the fact that it can be seen to be protruded 

 and retracted when the larva is feeding. It is also capable 

 of being altered in shape at will, so that it is either transversely 

 convex or flat. It is very generally kidney- shaped, with a 

 frontal triangular sinus which varies in depth and width in 

 different species. In some of the Ambulicine larvae (genus 

 Oxyambulyx) the ligula is very long and the sinus very deep 

 and narrow ; the structure then resembles in shape two 

 sausages joined at the base. The surface is smooth and set 

 with stout bristles, the position of which in Polyptychic 

 trilineatus sonanthis is shown in fig. 2 B. We are unable 

 to say if these bristles occupy the same position in all genera 

 and species. 



The mandible (fig. 2 A, g) is a strong, truncated, hollow 

 wedge, the base fitting into a socket in the skull near the base 

 of the antenna. The basal half is curved gently away from 

 the antenna, and the distal end is flattened, bevelled and 

 more strongly curved in the same direction, so that the 

 outer edges nearly face each other inwards and form the 

 cutting edges. In the first instar the cutting edges are 

 definitely toothed, but the teeth become less prominent 

 in later instars until, in the last instar, they have almost 

 disappeared, and are often represented only by transverse 

 grooves. 



The antenna (fig. 2 A, i) is composed of three segments. 

 Its base is set in a cavity of the skull into which the whole 



