INSECTS : THEIE FEET. 141 



some extent of being turned inside out, like tlie finger 

 of a glove. Partly around the blunt and truncate ex- 

 tremity are set two rows of minute hooks, occupying the 

 side next the middle line of the caterpillar in a semi- 

 circle along the margin. These hooks arch outward as 

 regards the axis of the pro-leg, though the majority of 

 them point towards the medial line of the body. The 

 double row is somewhat interrupted at its middle point ; 

 and just there, in each pro-leg, a clear vesicle or fleshy 

 bladder protrudes from the sole, which may perhaps 

 serve as a very delicate organ of touch, or may exude a 

 viscid secretion helpful to progress on smooth bodies. 

 The hooks seem adapted to catch and hold the fine 

 threads of silk, which most caterpillars spin as a carpet 

 for their steps. 



In some cases the circle of hooks is complete, as in 

 this example, which I find in one of the slides of my 

 drawer, marked " Pro-leg of a Caterpillar." It is some 

 large species, probably a Sphinx, for the hooks are 

 very large, of a clear orange-brown hue, and set in a 

 long oval ring — single as to their bases, but double 

 as to their points — completely around the extremity 

 of the foot. These hooks are simply cutaneous, as 

 may be well seen in this prepared specimen, — doubt- 

 less mounted in Canada balsam ; — ^for their origins are 

 mere blunt points, set most superficially in the thin skin 

 without any enlargement or apparent bulb. 



