INTRODUCTION. 53 



insects. They have six pectoral legs, eight abdo- 

 minal or membranous legs, and two anal ones, a 

 number corresponding to that of the majority of 

 butterfly larvae, to which also they are perfectly like 

 in structure. The body is usually rather narrow 

 anteriorly, and encreases slightly in diameter to the 

 eleventh or penultimate segment, which bears a 

 long dorsal horn, somewhat curved and having its 

 ]>oint directed backwards. In some cases two or 

 three of the anterior segments become rather sud- 

 denly attenuated towards the head, which thereby 

 acquires some resemblance to a pig's snout, and 

 has given occasion to the French name chenille* 

 cockonnes*. The surface is without hair, sometimes 

 % smooth, but more commonly shagreened, or covered 

 with hard grains like a piece of seal skin ; the 

 prevailing colour fine green, the sides often adorned 

 with oblique stripes of yellow, purple, or blue. The 

 caudal horn, which appears under a glass to be co- 

 vered with small points, arranged after the manner 

 of scales, has been conjectured to be a weapon of 

 offence or defence, but the animal has never been 

 observed to employ it for such purposes. When at 

 rest, they usually elevate the anterior part of the 

 body, and retract the head under the second or 

 third segment, thus assuming a peculiar attitude in 

 which they have been thought to bear some resem- 



* This form is exemplified in tbe caterpillars of Deilephila 

 Elpenor, D. Porcellus, and others belonging to the group which 

 we have distinguished as a subgenus under the name of Mi- 

 topsilug. 



