INSECT A. 223 



means of two principal trachese, extending, parallel to each 

 other, throughout the whole length of the body, having cen- 

 tres, at intervals, from which proceed numerous branches, 

 corresponding to external openings or stigmata(l), which ad- 



runs to the head, but which prevent it from retrograding-. At the lateral and an- 

 terior part of each chamber, are two transverse fissures which communicate with 

 the abdominal cavity and through which the blood contained in the latter enters 

 the heart. Each of these apertures is provided, internally, with a little semi-cir- 

 cular valve which presses on it during the systole of the heart. From this short 

 description it will be seen, that when the posterior chamber dilates, the blood 

 contained in the abdominal cavity penetrates into it by the transverse fissures of 

 which we have spoken, and which we call auriculo-ventriadaires. When the 

 chamber contracts, the blood finding no exit into the abdominal cavity forces the 

 inter-ventricular valve, passes into the second chamber which dilates to receive it, 

 and which, at the same time, receives a certain quantity of blood by the true auri- 

 culo-ventricular apertures. When the second chamber receives the contracting 

 impression, the blood passes into the third, which also receives a portion of it 

 through the lateral openings, and thus the blood is forced from one chamber to 

 another into the artery. It is these successive contractions of the chambers of the 

 heart that we perceive through the skin of caterpillars." The heart of the Crus- 

 tacea Decapoda, Squillse, Limuli, Araneae, &c.,as I have been assured by the same 

 profound observer, also contains similar valvulx. It is enclosed in a sort of sac or 

 pericardium, which, according to him, acts in lieu of an auricle. These divisions 

 or chambers of the dorsal vessel are what Lyonet terms ailes or wings; he also saw 

 that the dorsal vessel extended to the head, and terminated there in the manner 

 already described: but he did not see the orifices and valvuls mentioned by Straus. 

 The definition of the dorsal vessel given by this naturalist, evidently proves, that, 

 whatever be its internal formation, it is not a true heart. Besides, these observa- 

 tions do not teach us the true nature of the liquid it contains, nor how it becomes 

 diffused throughout the other parts of the body to effect their nutrition. It is 

 however certain, from the observations of Lyonet, that all the parts of the body 

 communicate with the corps graisseux by means of fibrilli. The trachex give off 

 branches which extend to the extremities of the various appendages of the body. 

 The action of the air may occasion the ascension of the nutritive juices in the 

 interstices, forming a sort of capillary tubes. 



(1) The number of segments in the body of the Myriapoda being undetermined, 

 that of their stigmata is the same, and frequently extends to above twenty. In the 

 Hexapoda it is frequently eighteen, nine on each side. This computation, how- 

 ever, is rather true with respect to the animal as a larva than in its perfect state. 

 Caterpillars, the larvx of the Coleoptera and those of various other Insects, have 

 one pair of stigmata on the first segment, or the one that bears the first pair of 

 legs; the second and the third are destitute of them, owing, I presume, to the 

 development of the wings which occurs in these rings, and renders the presence of 

 respiratory apertures useless in that particular place. The fourth and each cf the 

 seven following annuli exhibit a pair: but in coleopterous Insects in their perfect 

 state, besides the two anterior stigmata concealed in the cavity of the pro-thorax, 

 which had not been perceived, we observe two others, situated between the origin 



