124 EVENINGS AT THE MICROSCOPE. 



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 basis, but double as to their 

 points — completely around the extremity of the foot. 

 These hooks belong only to the skin, as may be well seen 

 in this prepared specimen, doubtless mounted in Canada 

 balsam; — for their roots are mere blunt points, set but 

 little below the surface of the thin skin, without any 

 enlargement or apparent bulb. 



