I METAMORPHOSES OF INSECTS 17 



They are soft and membranous,* and their forma- 

 tion is often exceedingly curious ; in every instance 

 they are only processes* of the exterior covering of 

 the insect. But the difference between the two kinds 

 which must be particularly pointed out is this. The 

 true legs are those which enlarge and otherwise 

 develop into the limbs of the future imago, whatever 

 be their size or variety of form, whereas the ab- 

 dominal legs are not persistent,* but are lost with 

 the cast skin during the metamorphosis of the larva 

 into chrysalis. Here then is a clue admitting of the 

 recognition with certainty of the individual segments 

 that compose the thorax, however much the distinc- 

 tion between them may have become obliterated in 

 course of development. Each pair of legs in the 

 perfect insect answers to each pair of true legs in the 

 larva. 



In the case of larvae that are destitute of true legs, 

 these wonderful organs have to be developed with all 

 their muscles and nerves during metamorphoses. 



The thorax,* which thus gives origin to the legs, is 

 usually large, and the union of the segments is firm 

 in proportion to the rest of the body. On the size of 

 these segments and their consolidation greatly de- 

 pends the strength of the insect. This region also 

 supports the wings ; to be precise, these appendages 

 are attached to the two hinder segments, the 

 meso*- and meta*-thorax. The development of the 

 thorax is not surprising, for there must be abun- 

 dant space within for the muscles which move the 

 organs for walking and for flight. There is little 

 trace of wings in the caterpillar, so that the formation 



C 



