232 NATURAL HISTORY. 
made up of long and delicate tubes. As lightness is a 
great object in the structure of the Insect, the digestive 
apparatus is made of as little bulk as possible. 
397. The feet of Insects are in conformity with their 
modes of life. Some have claws or hooks; some have 
a kind of suction cushion by which they can adhere to 
surfaces; some have fringed feet to enable them to 
swim; and some have their fore feet shaped for digging, 
like the Mole’s. 
398. The wings are generally made very much like 
those of the Bat, § 58. They consist of a double mem- 
brane over an extended slender frame-work. There are 
generally two pairs, but sometimes only one, as in the 
case of the common Fly. Often the first pair of wings 
are mere coverings for the other wings, and have no act- 
ive agency in flight. In this case they are made thick 
— and firm, and are called the 
elytra (singular elytrum). In 
Fig. 183 you see the elytra 
at a. When the Insect is at 
rest, the elytra are brought 
together over the back, the 
true wings being folded, some- 
times very curiously, under 
them. The true wings are 
light and thin, and they are 
transparent, except when they 
are covered with what ap- 
pears to the naked eye as a 
kind of colored dust, as is the case with the Moths and 
Butterflies. This dust, examined with the microscope, is 
found to be made up of little regularly-formed scales, 
often beautifully marked with lines. When they are 
rubbed off, their fastenings look, under the microscope, 
like the nail-heads on a roof when old shingles have been 
torn off. In some of the Butterflies’ the scales are ar- 
ranged like shingles on a roof, and with their various 
colors present a very beautiful appearance. 
Fig. 183. 
