76 INTERNAL ANATOMY OF INSECTS. 
Changes also take place in their internal organs. In 
the larvae the respiratory apparatus, especially the tra- 
cheal tubes, is often much larger and more ramified than 
in the imago ; and as the former is the principal jfeafc'ftjg 
state, there seems good ground for Mr. 13. Clark's opi- 
nion — that the respiration is intimately connected with 
the conversion of the food a . In the imago, there ap- 
pears to be more provision for storing up the air in vesi- 
cular reservoirs, than in the larva. Wonderful is the 
mode in which some of the changes in the internal struc- 
ture, which these variations indicate, must necessarily 
take place. They are, however, probably not more sin- 
gular than those which less obviously occur in the air- 
vessels of all insects in their great change out of the larva 
into the pupa state. But having before enlarged on this 
subject, I need not repeat my observations b . 
The access of air is as necessary to insects even in 
their egg state c , and in many cases its presence seems 
provided for with equal care, by means as beautiful as 
those Sir H. Davy and Sir E. Home have shown to oc- 
cur in the oxygenation of the eggs and foetuses of verte- 
brate animals d . It is only necessary to view the admi- 
rable net-work of air-vessels which Swammerdam disco- 
vered spread over the surface of the eggs of the hive-bee 
while in the ovaries e , — a provision which, from analogy, 
we may conclude obtains generally ; from the impor- 
* Iu Linn. Trans, iii. 302. " Vol. III. p. 195—. 
c Spallanzani found that the eggs of insects placed under the ex- 
hausted receiver of an air-pump, or in any small closed vessels, did 
not hatch, though every other condition for their development was 
present. Opusc. dc.Phj/s. i. 141. " Phllos. Trans. 1820. 213. 
p Bill. Xat. i. 204. b. t. xix./. 5. 
