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 feeding 

 state, there seems good ground for Mr. B. 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 6 , a provision which, from analogy, 

 we may conclude obtains generally; from the impor- 



;t In Linn. Trans, iii. 302. b 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^de. Phys.l. Ul. " Philos. Trans. 1820.J213. 



* Bibl. Nat. \. 204. b. /. xix,/. 5. 



