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 a . 

 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 c . 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. 



a Reaum. i. 145. Lyonet Anal. 10G . N. Diet. iVHist. Nut. 

 xvi. 224. PLATE XXI. FIG, 5. a. b See above, p. 90. note ". 

 c See above, p. 78. d Huber i. 273, 



