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. 8uch are the Cymeces, Grylli, &c. Finally, the remaining 
Insects provided with Avings, 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, Hymcnoptera, &c., 
these parts, though closely aj^proximated and in contact Avith 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, folloAving their contour 
in every direction, and forming, for each of them, so many moulds, 
like the envelope of a mummy, alloAVs 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 AAdiich the animal is shut up 
Many larvae, before they pass into their pupa state, prepare a cocoon 
in Avhich they enclose themselves, either Avith silk AAdiich they draAV 
from the interior of their bodies by means of the spinning apparatus 
of their lip, or other materials Avhich they collect. The perfect 
Insect issues from the nymph through a fissure or slit Avhich opens on 
the back of the thorax. In the pupae of Flies one of the extremities 
is detached, like a cap, to alloAV the egress of the animal. 
The larvae and pupae of those Insects Avhich experience a demi- 
metamorphosis only differ from the same in a perfect state, in the 
absence of Avings. 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 Avith that it is to possess in 
its perfect state. It is usually more elongated ; the head is frequently 
* The Pulex, the female MutiUa, the Working Anfs, and some feAv other Insects 
excepted. 
T Pupa obtecta, L. 
X Pupa courctata, L. 
