C6 
INTEODUCTIOJf. 
tions is ill tte number of feet, a circumstance which 
necessarily gives rise to diflFerent modes of progres- 
sion, and occasions striking differences in habit and 
appearance. Before alluding, however, to the num- 
ber and arrangement of the feet, it will be proper 
to mention what peculiarities are observable in the 
structure of these members. In many instances 
there is no fleshy plate at the extremity of the pro- 
legs capable of being expanded and contracted to 
serve the purposes of a foot, the leg being simply a 
conical fleshy prominence, having the extremity 
surrounded by a complete coronet of hooks. Ex- 
amples frequently occur in which the prolcgs have 
very much the appearance of a rvoodm leg, the upper 
part being thick, succeeded by a slender cylindrical 
piece which terminates in a circular expansion sur- 
rounded with crotchets, and having a small nipple 
in the centre which holds the place of a foot. 
Although these small hooks are generally present, 
this does not seem to be universally the case, for 
the subcutaneous lai-va3 of a small moth of the 
Liimean genus Tinea, and a few others, are said to 
be without them. The true, or pectoral legs, are 
always six in number, and nearly uniform in figiue ; 
the most remarkable among the few exceptions to 
this, is to be foimd in the caterpillar of the Lobster- 
moth, which has the two posterior pairs greatly 
elongated and terminating in a land of claw. The 
amount of abdominal legs, however, is very variable 
in different groups, and in the anomalous caterpillars 
of two small bromiish-yellow moths ( Hetei'ogenea 
