Page:Jardine Naturalist's library Entomology.djvu/315

Rh more than sixteen feet, while the larvæ of saw-flies have generally from eighteen to twenty-two; a few have only six, a circumstance which again distinguishes them from true caterpillars, in which the number of these parts is never below ten. Another mark of distinction is afforded by the structure of the feet. In lepidopterous larvæ the abdominal legs are surmounted by a coronet of small hooks, appendages which are never found in those of false caterpillars, as the latter are simply mammiform protuberances. This minute difference, which can only be detected by the microscope, has however a material influence over the habits of the respective caterpillars, which often enables us to distinguish them at first sight. The coronet of hooks converts the membranous or abdominal legs of true caterpillars into efficient instruments of prehension, and they accordingly fix their body by means of them to the plane of position, while the head and anterior part remain free. The abdominal legs of the others, on the contrary, are mere points of support, incapable of clinging to an object, and the larva consequently fixes itself by its pectoral or forelegs, which are much developed for the purpose. The whole of the abdominal portion of the body is thus left at liberty, and it is either borne curved inwards, (as in the gooseberry saw-fly,) or projects into the air in variously contorted and singular postures, as is remarkably exemplified in the willow saw-fly, (Nematus Capreæ,) and the larva of Hylotoma Rosæ, which has the extremity of its