INTERNAL ANATOMY OF INSECTS. 151 
flames; in colour it is most commonly white, but some- 
times yellow or green. It is imagined to be a kind of 
epiploon or caul, and is accumulated in the larva as a 
store of nutriment for the growth and development of the 
organs of the perfect insect while in the pupa state 3 . 
The blood in which the different organs float that is 
not required for their nutriment, is supposed to be ex- 
pended in the formation of this substance. Marcel de 
Serres is of opinion that it is secreted from the chyle by 
passing through the pores of the dorsal vessel, formerly 
called the heart of insects b . 
Under this head I may mention what little is known 
with regard to the perspiration of these animals . That 
a considerable quantity of fluid passes off from them 
when in the pupa state, is sufficiently proved by the loss 
of weight which they undergo, and by the experiments 
of Reaumur, who collected the fluid in closed glass 
tubes ; and that in their perfect state they are constantly 
passing off' perspirable matter by the pores of their skin 
or crust, is not only rendered probable by the succulent 
nature of their food and the absence of any urinary dis- 
charge, but is proved by what takes place in a swarm of 
bees. These insects, when crowded together in hot 
weather in a large mass, become heated to such a degree, 
and perspire so copiously, that those near the bottom 
are quite drenched with the moisture it produces, which 
so relaxes their wings that they are unable to fly d . 
I am, &c. 
■ Reaum. i. 145. Lyonet Anat. 100—. N. Diet. cl'IIisf. Nat. 
xvi. 224. Plate XXI. Fig. 5. a. b See above, p. 90. note ". 
c See above, p. 78. ' Huber i. 2/3. 
