INTERNAL ANATOMY OF INSECTS. a7 
plants, and some of them embedded in the very substance 
of a leaf or twig*, are in a situation for the abundant 
absorption of oxygen: and the pouch of silk in which 
the eggs of spiders and Hydrophili are deposited, may 
probably, from Count Rumford’s experiments, be of uti- 
lity in the same point of view. In the case of the Tri- 
choptera and other insects whose eggs are dropped into 
the water enveloped in a mass of jelly, this substance per- 
haps serves for aérating the included embryo, in the same 
way with the jelly surrounding 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 tobe*. It is not im- 
probable that the singular rays that terminate the eggs 
of Nepa? may in some way be connected with the aéra- 
tion of the egg. 
To what I have before remarked with regard to the 
vital heat of insects*, 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‘. A con- 
firmation of this remark is afforded by Inch, a German 
writer, who, upon putting a thermometer into a bee-hive 
in winter, found it stand 27° higher than in the open air; 
in an anthill, he found it 6° or 7° higher; in a vessel 
containing many blister-beetles, (Cantharis vesicatoria 
Latr.) 4° or 5° higher. A thermometer, standing in the 
air at 14° R.; put into a glass vessel with Acrida viridis- 
* Vou. I. p. 449—. III. p. 76. > Ibid. 68—. 
© Philos. Trans. 1820. 218. 4 Vou. III. p. 94. 
© Vor. I. p. 229—. £ Tbid. p, 214. 
