VJ6 On the Uses of the Dorsal Vessel. [March, 



another when the contraction was at its maximum. In the grass- 

 hopper, on the contraiy, the contractions carried these membranes 

 scarcely one-fourth of the diameter of the dorsal vessel. The 

 motion perceived in the bremus terrestris was rather a continual 

 pulsation than a contraction and dilatation of the membranes of the 

 dorsal vessel. These pulsations, which 1 reckoned at 140 in a 

 minute, but which in reality arc much more frequent, proceed 

 from the bottom to the top, and are very irregular. The contrac- 

 tions and dilatations of the dorsal vessel are so strong in the cater- 

 pillars that they shake all their peritoneal membrane and their 

 adipose tissue ; v/hich never takes place in the perfect insects. It is 

 obvious that when the dorsal vessel contracts, its diameter must 

 diminish, while it increases in the dilatations. 



The dorsal vessel is maintained in its position by muscular fibres, 

 which in general are disposed in triangles, and which increase in 

 breadtli from the superior part of the body to its inferior extremity. 

 The muscular fibres have been called wings by Lyonnet, because 

 they form a kind of appendix, which puts one in mind of that 

 organ. These appendices, formed of muscular strings, contain a 

 great number of very small fatty molecules, and some nerves ; but 

 these muscular strings, when carefully examined before the micro- 

 scope, appear composed of very line and close transverse fibres. 

 Besides these fibres, we see that the fatty matter is contained in a 

 very extensible cellular substance. It is in the numerous cells of 

 this substance that we find a very abundant adipose matter, the 

 colour of which, always analogous to that of the dorsal vessel, is 

 distinguished from the white and more animahzed fat contained in 

 the peritoneal membrane. We may conclude that this fat is more 

 animalized than that which touches the dorsal vessel, because its 

 properties are nearly similar to that of animals with vertebrae. 



The colour of this fatty substance is almost always the same. It 

 is generally white, and varies only in its shade from snow-white to 

 yellowish-white. Its odour is faint, seldom disagreeable, and 

 often almost nothing. It has no action on vegetable colours. 

 It is very dense j and when disengaged from the membrane 

 that contains it, it falls to the bottom of water. When ex- 

 posed to the air, it becomes yellow and rancid, yielding a portion 

 of its carbon and hydrogen to the oxygen of the air. I cannot say 

 whether, as is the case in animals with vertebrae, the fat of frugi- 

 vorous insects is firmer than that of carnivorous insects. All the 

 acids act on the fat of insects with more or less energy. Sulphuric 

 acid chars it very readily, as I have observed in the fat of the 

 lomhyx pavonia major. The fat of the larva of this species dried 

 in the air, and of consequence become rancid, and then acted upon 

 by sulphuric acid, gives that acid a strong yellow colour, and does 

 not char very quickly. When the fat of insects is treated with 

 nitric acid, a little nitrous gas is exhaled. The fat becomes yellow, 

 coagulates ntpidly, combines with a certain quantity of oxygen, and 



