INTERNAL ANATOMY OF INSECTS. 77 



tance which nature has attached to the oxygenation of 

 the germ while in the matrix. And judging from ana- 

 logy, we may infer that the access of this element is as 

 carefully secured after the egg is laid, as before. The 

 eggs of most insects being of a porous texture, often at- 

 tached to the leaves of plants, and some of them embed- 

 ded in the very substance of a leaf or twig a , are in a 

 situation for the abundant absorption of oxygen : and 

 the pouch of silk in which the eggs of spiders and Hy- 

 drophili are deposited, may probably, from Count Rum- 

 ford's experiments, be of utility in the same point of view. 

 In the case of the TricJioptera and other insects b whose 

 eggs are dropped into the water enveloped in a mass of 

 jelly, this substance perhaps serves for aerating the in- 

 cluded embryo, in the same way with the jelly surround- 

 ing the eggs of the frog, dog-fish, &c. It would be 

 desirable to ascertain whether the former jelly be of the 

 same nature as the experiments of Mr. Brande have 

 shown the latter to be c . It is not improbable that the 

 singular rays that terminate the eggs of Nepa d may in 

 some way be connected with the aeration of the egg. 



To what I have before remarked with regard to the 

 vital heat of insects e , I may under this head very pro- 

 perly add a few further observations. I there stated, that 

 the temperature of these animals is usually that of the me- 

 dium they inhabit, but that bees, and perhaps other gre- 

 garious ones, furnish an exception to this rule f . A con- 

 firmation of this remark is afforded by Inch, a German 



a VOL. I. p. 446. III. p. 76. b Ibid. 68. 



c Philos. Trans. 1820. 218. d VOL. III. p. 94. 



e VOL. II. p. 228~. f Ibid. p. 211. 



