328 
INSECTS. 
parallel to each other, throughout tlie whole length of the body- 
having centres, at inteivals, from which proceed numerous branches, 
corresijonding 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 enters 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 w'hich we have spoken, and which vve call auriculo-ventriculairies. 
When the chamber contracts, the blood finding no exit into the abdominal cavity 
forces the inter-veatricidar 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-veutrieular apertures. When the second chamber receives the contract- 
ing impression, tlie 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 centractions of the chambers of the heart that 
we perceive through the skin of caterpillars.” The heart of the Crustacea Decapoda, 
Squilli, Liinula;, Araneae, &c., as I have been assured by the same profound 
observer, also contains similar valvulfe. It is enclosed in a sort of sac or pericar- 
dium, w hicii, according to him, acts in lieu of an auricle. These divisions or chambers 
of the dorsal vessel ai-e 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 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 diffused 
throughout the other parts of the body to effect their nutrition. It is however certain, 
from tlie observations of Lyonet, that all the parts of the body communicate with the 
corps yruisseux by means of fibrilli. The tracheae 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 animal as a larva than in its perfect state. Cater- 
pillars, the larva; 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 tremaeres. 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 Libeliulae, 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 Pentatoma;, 
and Scuteilerse is provided iuferiorly with a pair of stigmata. In the apterous Spec- 
