LEP/DOPTERA. 145 



meet each other ; the bites succeed each other quickly ; there is not 

 one, or scarcely one of them, that does not detach a bit, and each 

 bit is swallowed almost as soon as cut off. At each fresh bite the 

 head approaches the legs in such a way that during the succession of 

 bites it describes an arc ; it hollows out the portion of the leaf in a 

 segment of a circle, and it is always in this order that it gnaws it." 



But there is a phenomenon in the life of caterpillars which we 

 ought to point out, and which has attracted the attention of the most 

 illustrious observers. All caterpillars change their skins many times 

 during their life. It is not, indeed, enough to say that they change 

 their skins ; the skins or cases they cast are so complete that they 

 might be taken for entire caterpillars. The hairs, the case of the 

 legs, the claws with which the legs are provided, the hard and solid 

 parts which cover the head, the jaws all these are found in the 

 skin which the insect abandons. What an operation for the poor 

 little animal ! This labour is so enormous, so troublesome, that one 

 cannot form a just idea of it. One or two days before this grand 

 crisis, the caterpillar leaves off eating, loses its usual activity, and be- 

 comes motionless and languid. Their colour fades, their skin dries 

 little by little, they bow their backs, swell out their segments. At 

 last this dried-up skin splits below the back, on the second or third 

 ring, and lets us have a glimpse of a small portion of the new skin, 

 easily to be recognised by the freshness and brightness of its colours. 



" When once the split has been begun," says Reaumur, " it is 

 easy for the insect to extend it ; it continues to swell out that part 

 of its body which is opposite the slit. Very soon this part raises 

 itself above the sides of the split ; it does the work of a wedge, which 

 elongates it; thus the split soon extends from the end or the com- 

 mencement of the first ring as far as the other side of the end of the 

 fourth. The upper portion of the body which corresponds to these 

 four rings is then laid bare, and the caterpillar has an opening suf- 

 ficiently large to serve it as an egress through which it can entirely 

 leave its old skin. It curves its fore part, and draws it backwards ; 

 by this movement it disengages its head from under its old envelope, 

 and brings it up to the beginning of the slit ; at once it raises it, and 

 puts it out through this slit. The moment afterwards it stretches 

 out its fore part and lowers its head. There now remains for the 

 caterpillar nothing but to draw its hinder part from the old case." 



This excessively laborious operation is finished in less than a 

 minute. The new livery which the caterpillar has just put on is fresh 

 and bright in colour. But the animal is exhausted by its fast, and 

 the efforts which it has made. It requires a few hours in which to 



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