GENERAL INTRODUCTION. 13 



The horn appears to have developed from a pair of tubercles 

 on segment 12. The tubercles are most strongly developed 

 in the subfamilies Acherontiin^: and Ambulicin^, and 

 are largest on the dorso-lateral line and on the oblique stripes : 

 they are least in evidence in the subfamily Chcerocampesle, 

 and their presence or absence is of considerable phylogenetic 

 importance. They are often present on segment 2 and on 

 the anal flap and claspers when entirely wanting elsewhere. 

 They are frequently wanting in the newly -hatched larva, 

 but may develop in later instars ; more rarely the reverse 

 occurs. They develop rarely into long fleshy spines or 

 processes, as mentioned above. 



The spiracles are always oval in shape, with a central longi- 

 tudinal slit and often a raised chitinous rim. Those on 

 segments 2 and 12 are usually larger than the rest, and that 

 on 12 is placed obliquely, the long axis roughfy on a line 

 drawn from the base of the horn to the lower edge of the 

 front margin of the segment. The remaining spiracles have 

 the long axis at right angles to the dorsal line of the larva. 



Chsetotaxy. — We have, unfortunately, not studied the 

 hairs of the newly-hatched larva? of many of the species we 

 have bred, but in the case of Clanis phalaris they are arranged 

 in small groups ; in Cephonodes and Gurelca they are branched ; 

 in Sataspes infernalis they are bifid ; in Rhopalo psyche 

 nycteris they are simple ; the compound hairs in each case 

 becoming simple in the second or third instar. The secondary 

 hairs are sometimes wanting. The body of the larva in the 

 last instar is covered with minute hairs, amongst which, 

 on each segment, there are some much larger ones which 

 we call the main hairs. The minute secondary hairs are 

 arranged, usually in a single row, along the secondary rings. 

 On segment 2 there are two transverse rows of main hairs, 

 one row close to the front margin and another row at about 

 the middle of the segment ; on segments 3 and 4 there is 

 one row at about the middle of the segment ; each row is 

 composed of four hairs on each side of the dorsal line — one 

 subdorsal, one dorso-lateral, one supra- and one subspiracular. 

 On the remaining segments the hairs are not in a row ; on 

 5 to 11 the subdorsal hairs are in front, usually on the third 

 secondary ring, the dorso-lateral hair being behind on the 

 sixth ring : the supraspiracular hair is just above and in 

 front of the spiracle, and the subspiracular below the spiracle ; 

 the two upper pairs of hairs form what is called the dorsal 

 trapeze. On 12 the dorsal trapeze is arranged differently, 

 the dorso-lateral pair of hairs being in front and the subdorsals 

 behind ; on 14 the trapeze is similar to that on 12 except 

 that the subdorsals are at the very end of the anal flap ; 



