INTRODUCTION. (39 



the thorax of the winged insect — and the others are 

 attached to the sixth, seventh, eighth, ninth, and anal 

 segments. The form of the anterior or thoracic legs 

 is wholly unlike that of the others, and they seem 

 to he the principal instruments of locomotion. They 

 are of a horny substance, wide at the base, and gra- 

 dually growing narrower to the lower extremity, 

 where they terminate in a strong claw. Each of 

 them is divided into several segments, which corre- 

 spond to the different parts that compose the leg of the 

 future fly. (Plate II. fig. 1, represents a pair of these 

 legs). The other legs, attached to the hinder or ab- 

 dominal portion of the body, are soft and fleshy, and 

 therefore have been called the membranous legs, or 

 pro-legs. Their principal use is to support the bo- 

 dy, by adhering to the slender twigs and shoots 

 which the animals frequent to procure their food. 

 For this purpose they can be lengthened and short- 

 ened at pleasure, and can even be drawn almost 

 within the body, like the horns of a snail. Their 

 general figure approaches to that of a truncated cone, 

 which is terminated by a fleshy foot of a construction 

 peculiarly fitted to cling to a smooth surface, or em- 

 brace a slender twig. What may be called the sole 

 of the foot, expands into a somewhat triangular 

 plate, which is furnished on its inner edge with a 

 row of small horny hooks or claws, consisting of a 

 short and long one alternately, forming, as Reau- 

 mur remarks, a kind of palisade round part of the 

 circumference. When the disk, or central plate of 



