328 INSECTA. 



parallel to each other, throughout the whole length of the bod}*", 

 having centres, at intervals, from which proceed numerous branches, 

 corresponding to external openings or stigmata*, which admit air. 



two transverse fissures which communicate with the abdominal cavity and through 

 which the blood contained in the latter eaters the heart. Each of these apertures is pro- 

 vided, internally, with a little semi-circular valve which presses on it during the systole 

 of the heart. From this short description it will be seen, that when the posterior cham- 

 ber dilates, the blood contained in the abdominal cavity penetrates into it by the 

 transverse fissures of which we have spoken, and which we caU auriculo-ventriculmries. 

 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 auriculo-veutricular apertures. When the second chamber receives the contract- 

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

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

 into the artery. It is these successive centractions of the chambers of the heart that 

 we perceive through the skin of caterpillars." The heart of the Crustacea Decapoda, 

 Squilli, Limulse, Araneae, &c., as I have been assured by the same profound 

 observer, also contains similar valvulae. It is enclosed in a sort of sac or pericar- 

 dium, 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 seethe orifices and valvulae mentioned by Straus. The 

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

 ever be its internal formation, it is not a true heart. Besides, these observations do 

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

 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 graisseiix by means of fibrilli. The trachea; 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. 



* 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 Hexa- 

 poda it is frequently eighteen, nine on each side. This computation, however, is 

 rather true with respect to the lu.imal as a larva than in its perfect state. Cater- 

 pillars, the larvse 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 developement 

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

 apertures useless in that particular place. The fourth and each of the seven follow- 

 ing 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 of the elytra and 

 that of the wings : they belong to the mesothorax. There are none in the metatho- 

 rax, unless we consider the two of the first abdominal segments, as supplementary 

 to the thorax, a consideration founded on what occurs in the Diptera and Hymenop- 

 terous Insects with a pediculated abdomen, where these two stigmata, with the 

 semi-segment in which they are placed, make part of the thorax. Thus, generally 

 speaking, the hexapoda have eight pairs of abdominal stigmata, the two last of 

 which, however, are frequently obliterated. 



In Acrydium, Truxalis, and Libellula, each side of the mesothorax presents a stig- 

 ma, or those which Marcel de Serres calls fremaeres. In these latter Insects, as 

 well as in others with naked wings, or without elytra, the two first thoracic stigmata 

 are placed above, between the prothorax and the mesothorax. With the exception of 

 the Libellulae, the thorax proper offers no other distinct stigmata — I say thorax proper, 

 because, as we have already observed, the two first of the abdomen, in several, are 

 referable to the posterior extremity of the thorax. The metathorax of the Pentatomae, 

 and Scutellerae is provided inferiorly with a pair of stigmata. In the apterous Spec- 



