INSECTA. 239 



pare a cocoon in which they enclose themselves, either with 

 silk which they draw from the interior of their bodies by 

 means of the spinning apparatus of their lip, or other mate- 

 rials which they collect. The perfect Insect issues from the 

 nymph through a fissure or slit which opens on the back of 

 the thorax. In the pupae of Flies one of the extremities is 

 detached, like a cap. to allow the egress of the animal. 



The larvae and pupae of those Insects which experience a 

 demi-metamorphosis only differ from the same in a perfect 

 state, in the absence of wings. The other external organs 

 are precisely alike. But in such as undergo a complete meta- 

 morphosis, the form of the body of the larva has no constant 

 relation with that it is to possess in its perfect state. It is 

 usually more elongated ; the head is frequently very different, 

 as well in its consistence as in its figure, having mere rudi- 

 ments of antennae or perhaps none at all ; there are never any 

 compound eyes. 



There is also a great disparity in the organs of manducation, 

 as may be easily seen by comparing the mouth of a caterpillar 

 with that of the Butterfly, or the mouth of the larva of a Fly 

 with that of the perfect Insect. 



Several of these larvae are destitute of feet; others, such as 

 the caterpillars, have many, all, the six first excepted, mem- 

 branous, and without terminal hooks. Some Insects, such as 

 the Ephemerae, exhibit a singular anomaly in their metamor- 

 phosis the animal arrived at its perfect state undergoes 

 another change of tegument(l). 



The Insects which constitute our three first orders pre- 

 serve for life their natal form. The Myriapoda, however, 

 exhibit a kind of metamorphosis. At first they have but six 

 legs, or, according to Savi, are altogether destitute of them ; 



(1) " Se depouillent encore de leurs ailes," is the unguarded expression of our 

 author. It is not the wings alone, but the entire animal, after attaining its perfect 

 condition, that is thus divested of its external pellicle, even t<Pthe slender, seta- 

 ceous appendages which terminate the posterior extremity of the body. It is the 

 common May-fly of our country. Am. Ed. 



