GENERAL INTRODUCTION. 11 



colourless, with a black pupil, and the base often reddish - 

 brown or black in colour. 



We call the uppermost eye no. 1, and number the rest 

 downwards. Eye 2 is a little below and on the inner side 

 of 1 ; 3 is below and slightly on the inner side of 2 ; 4 is 

 well below and slightly on the outer side of 3 ; 5 is slightly 

 below 4, and on the outer side of all the rest ; 6 is the lowest, 

 and is situated on the under surface of the head near the base 

 of the antenna, directed downwards. Eyes 1 to 4 lie on a 

 curve convex to the base of the mandible, 3, 4 and 6 always 

 more or less in a straight line, with 6 at a greater distance 

 from 4 than the latter is from 3 ; 5 is always on the outer 

 side of 4 and 6 ; 4, 5 and 6 often lie at the corners of an 

 equilateral triangle. Within these limits the arrangement 

 of the eyes varies in different species, and the size of the eyes 

 also varies. 



The surface of the head may be dull or shining and polished ; 

 it may be smooth or covered more or less closely with seti- 

 ferous tubercles, and between these there may be superficial 

 corrugations or reticulations ; in addition to the bristles 

 on the labrum, ligula and antenna already mentioned, there 

 are main hairs arranged very similarly to those on the body 

 segments — one on each side of the apex of the false clypeus, 

 one on each side at its middle, and one on each side near 

 the base of the true clypeus. 



The body in the first iustar has the same shape in all 

 subfamilies. It is always cylindrical, with a straight bifid 

 horn, the diameter of the body and the length of the horn 

 varying with reference to the length of the body in different 

 species. In the full-fed larva the shape varies with the sub- 

 family. In the Ach~erontiin.e the body is nearly cylindrical, 

 tapering only slightly from segment 7 to the large rounded 

 head ; in the Ambtilictn^e the body tapers more sharply 

 from segment 5 to the large triangular head ; the Sesiin^e 

 larvae either resemble those of the Ambulicinje or have 

 bodies nearly cylindrical ; the larvae of the subfamilies 

 Philampelin^ and Chgeroc ampins taper sharply forwards 

 from segment 5 to a small rounded head, and segments 4 

 and 5 are sometimes tumid and, more rarely, laterally flanged. 

 Except for the horn, important processes of any kind are 

 rare in Hawk-Moth larvae ; in the genus Polyptychus the newly- 

 hatched larva has a dorsal prominence on segment 14, but it 

 disappears in the later instars ; Pseudodolbina fo has long- 

 fleshy tubercles on segments 3, 4 and 14 ; in a larva recently 

 discovered by us (Apocalypsis velox) some of the tubercles 

 are developed into long fleshy spines ; Meganoton nyctiphanes 

 has a fleshy hump on 3. The proportional lengths of the 



