INTRODUCTION. 
69 
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 be 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. I, 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 he drawn almost 
within the body, like the horns of a snail. Their 
general figure approaches to that of a truncated cone, 
which is terminated hy 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 
