THIRD 
GREAT DIVISION 
OP THE 
ANIMAL KINGDOM. 
(continued.) 
C LASS III. 
INSECTA. 
Insects, which form tlie third class of articulated animals provided 
with articulated legs, have, besides, a dorsal vessel analogous to the 
vestige of a heart, but totally destitute of any branch for the circida- 
tion*. They respire by means of two princi])al tracheae, extending. 
* Anatomists are greatly divided with respect to the nature of this organ ; some 
consider it as a true heart ; others, among whom is the Baron Cuvier, deny it this 
quality, an opinion which appears to us to he fully confirmed by the admirable re- 
searches of M. Marcel de Serres — “ Memoire Sur le Vaisseau Dorsal des Insectes ” 
— published in the Mdm. du Mus. d’Hist. Nat. Aceonling to the latter it secretes 
fat, w'hieh is subsequently elaborated in the adipose tissue which surrounds it. 
Lyonct says that it contains a gummy substance of an orange colour. Some very 
reeent observations appear to establish the existence of certain very small vessels ; 
but in addition to the fact that this circulation must be very partial. Insects 
w’Oidd still greatly differ, in this respect, from the Crustacea, inasmuch as the 
blood does not return to the heart. M. Straus in his report — Bullet. Univers., de 
M. le Baron de Fdrussac — on a Memoir of M. Hdrold on this subject, has inti- 
mated his own opinion on the matter as deduced from his anatomical investigations 
of the Melolontha. “The dorsal vessel,” says that gentleman, “is the true 
heart of Insects, being, as in the higher animals, the locomotive organ of the 
blood, which, instead of being contained in vessels, is diffused throughout the 
general cavity of the body. This heart occupies all the length of the back of the 
abdomen, and terminates anteriorly by a single non-ramified .artery which carries 
the blood into the head where it diffuses it, and whence it returns into the abdomen 
in consequence of its accumulation in the he.ad, to again enter the heart ; to this 
all the circulatioiT’in Insects is reduced, they having merely a single artery without 
branches and no veins. The alre of the heart are not muscular as is asserted by 
Herold they are merely fibrous ligaments which keep the dorsal vessel in its place. 
The he.art, that is to say the abdominal part of the vessel (in the Melolontha viilyaris) 
is divided, internally, into eight chambers, separated from each other by two con- 
verging valvulw, which allow the transmission of the blood from behinil forwards, and 
from one chamber to another, into the artery which runs to the head, but which 
prevent it from retrograding. At the lateral and anterior part of each chamber, are 
