20 TRANSFORMATIONS OF INSECTS. 



of five pairs of them. The absence of the central legs produces 

 the curious appearance of these well-known insects. In the 

 engraving the fore-legs are also shown, but they are very small 

 and pointed, whilst the two pairs of membranous legs are short 

 and distinct. 



The wings exist in the great majority of perfect insects. They 

 are four in number, and are in two pairs : one is attached to the 

 mesothorax and the other to the metathorax. One of the largest 

 divisions of the class of insects (the Dipterd) is supposed to contain 

 species that only have two wings ; but the wings of the second pair 

 do exist, although they are in a very rudimentary condition. 



In most insects the wings are either like a transparent mem- 

 brane, or are covered with dusty scales of microscopic size, the 

 whole being- stretched upon hard radiating nervures ; but in one 

 entire order the anterior wings have the consistence of the skin 

 of the body, and form a sort of case to the upper parts of the 

 insect. The membrane of the wings is to all appearance simple, 

 but it is really double. There is no trace of a wing, or anything 

 approaching to it, in the caterpillar, but the shape of the thorax 

 of the chrysalis indicates that these wonderful organs are in course 

 of formation whilst it is motionless and inactive. Immediately 

 after the chrysalis fs formed, and just before the caterpillar's skin 

 which covers it for a while is burst and detached, the wings and 

 some other organs may be traced in a very rudimentary condition. 

 Reaumur has. given the two accompanying views of chrysalides, 

 to show the wing cases in their natural position, and when removed 

 by a little management with the antennae from the lately-formed 

 pupa. When the butterfly bursts forth from the skin of the 

 chrysalis, its wings are often so moist and so unfinished that it is 

 easy to see they are formed of two membranes, between which 

 run the nervures which enable the insect to move them in its 

 flight. 



The heads of insects are composed, like the other portions of 

 the body, of several segments ; but, although this is a fact, its 

 demonstration has not been satisfactorily completed. At the 

 birth of the larva no satisfactory division of the head into seg- 

 ments can be detected ; but knowing, as we do, that each pair 

 of appendages — legs and wings — is attached to a particular seg- 



