340 INSECTA. 



are apterous issue from the ovum with the form they are always to 

 preserve*: they are said to be without a metamorphosis. Of those 

 that have wings, many experience no other change than that of 

 receiving them : these are said to undergo a demi-metamorphosis. 

 Their larva resembles the perfect insect, with the single exception of 

 the wings, which are totally wanting. The nymph only differs from 

 the larva in possessing stumps or rudiments of wings, which are 

 developed at its final change of tegument, and render the animal per- 

 fect. Such are the Cymeces, Grylli, &c. Finally, the remaining 

 Insects provided with wings, that are said to undergo a complete meta- 

 morphosis, are at first larvce, resembling caterpillars or Worms, and 

 then become motionless nymphs, but presenting in that state all the 

 parts of the perfect insect contracted, and as if wrapped in a bandage. 



In the nymph of the Coleoptera, Neuroptera, Hymenoptera, &c., 

 these parts, though closely approximated and in contact with the 

 body, are free ; but they are not so in that of the Lepidoptera and of 

 many Diptera. An elastic or solid skin is moulded over the body 

 and its external parts, forming a kind of case for it. 



That of the chrysalides of the Lepidoptera merely consisting of a 

 simple pellicle applied to the external organs, following their contour 

 in every direction, and forming, for each of them, so many moulds, 

 like the envelope of a mummy, allows us to recognise and distinguish 

 themf; but those of Flies and Syrphi, formed of the dried skin of 

 the larva, resemble an egg-like shell. It is a species of capsule or 

 case in which the animal is shut up J. 



Many larvae, before they pass into their pupa state, prepare 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 materials 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 metamorphosis, 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 



* The Pulex, the female Mutillce, the Working Ants, and some few other Insects 

 excepted. 



f Pupa obtecta t L. 

 J Pupa coarctata, L. 



