EXTERNAL ANATOMY OF INSECTS. 591 
applied to a more recent one of a celebrated French 
writer, who seems to think their origin and structure 
a€rostatic, that they are auxiliary to the legs, and bor- 
rowed in part from the respiratory organs*. Oken thinks 
that they are exsiccated gills®. Were I disposed to 
enter into these subtile speculations, I might here recall 
your attention to the analogy that, in their metamor- 
phoses, exists between the Saurian Reptiles or lizard 
tribe and insects, and conjecture that the wings of the 
Draco are really representatives of the mid-legs of Hexa- 
pods, thus preparing to disappear altogether ; but I shall 
content myself with throwing out this hint, which you 
are welcome to pursue. The organs of flight in ge- 
neral may be considered as to their number, kinds, and 
composition. 
i. Number. The most natural number is four, for this 
obtains in the majority. In almost every Order, indeed, 
there occur instances of insects that have solely a single 
pair or none °. 
These, however, are only exceptions to the rule; but 
in the Diptera, unless we consider the alula, the repre- 
sentatives of the secondary wings 4%, as a distinct pair, 
he alludes (411); namely, that in that state they consist of two seg- 
ments more than in the imago ; these follow the three pedigerous 
segments, have no pro-legs, and are supposed to belong to the trunk 
rather than totheabdomen. To make this circumstance bear upon 
the question, it must be proved that in the perfect insect these seg- 
ments in some manner become the back of the trunk and bear the 
wings. This would not be more wonderful than many changes that 
are known to occur in insects. 5 
* Latreille, Organisation extérieure des Ins. 173—. 
> Carus. Introd. to Anat. Comp. ii. 398. Engl. Tr. 
© For instance Meloe, the female glow-worm, Lygeus brevipennis, 
Ephemera diptera, Cynips aptera, neuter ants, &e. &e. 
4 See above, p. 557. 
