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 naiTow 
anteriorly, and encreases slightly in diameter to the 
eleventh or penultimate segment, which hears a 
long dorsal horn, somewhat curved and having its 
point directed backwards. In some cases two or 
three of the anterior segments become rather sud- 
denly attenuated towards the head, which tliereby 
acquires some resemblance to a pig’s snout, and 
has given occasion to the French name chenilles 
cochonnes*. 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 stiipcs 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 
©fience or defence, hut 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 imder 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 the caterpillars of DeilephUa 
Elpenor^ D. PorceUtts^ and others belonging to the group which 
we have distinguished as a subgenus under the name of iWa- 
topsilus. 
