COMPARATIVE ANATOMY. 
The itructure qf this part is very diffe- 
rent in the turtle, and has given rise to 
more controversy than that of any order 
of animals. Their heart possesses two au- 
ricles, which are separated by a complete 
septum, like those of warm-blooded ani- 
mals, and receive their blood in the same 
manner as in those animals, viz. the two 
venae cavae terminate in tlie right anricle, 
the pulmonary veins in tiie left. Each 
pours its blood into the corresponding ven- 
tricle, of M'hich cavities there are two : 
thus the structure of the heart hitherto re- 
sembles that of mammalia. 
The characteristic peculiarities which 
distinguish tire heart of these animals, con- 
sist in two circumstances : first, both tlie 
ventricles communicate together; there is 
a muscular, and as it were tubular valve, 
going from the left to the right cavity, by 
means of which the former opens into the 
latter. Secondly, the large arterial trunks 
arise all together from the right ventricle 
only, (no vessel coming from the left.) 
The aorta forming three grand trunks, is 
situated towards the right side and the up- 
per part ; the pulmonary artery comes as 
it were from a particular dilatation, which is 
not situated in the middle of the basis of 
the heart, but lower ; (it must be under- 
stood, that we apply these terms according 
to the horizontal position of the animal.) 
We can now comprehend how tins won- 
deiful and anomalous structure, by which 
all the blood is propelled from the right 
ventricle only, is accommodated to the pe- 
culiar way of life of the animal, vyhich sub- 
jects it frequently to remaining for a long 
time under water. For the greater circu- 
lation is so far independent of that which 
goes through the lungs, that it can proceed 
while the animal is under water, and there- 
by prevented from respiring, although tlie 
latter is impeded. In warm blooded ani- 
mals, on the contrary, no blood can enter 
the aorta, which has not previously passed 
through the lungs into the left ventricle ; 
and hence an obstruction of respiration 
most immediately influences the greater 
circulation. 
The heait in this class of animals is ex- 
tremely small in proportion to the body. 
Its structure is very simple, as it consists 
of a single auricle and ventricle, which 
correspond with the right side of the heart 
in warm-blooded animals. The ventricle 
gives rise to a single arlerial trunk, (wliich 
is expanded in most fishes into a kind of 
bulb as it leaves the heart,,) going straight 
fonvards to tlie branchia?, or organs of ras- 
pu-ation. The blood passes from these into 
a large artery, analogous to the aorta, 
which goes along the spine and supplies 
the body of the animal. It is then returned 
by tlie venae cavae into the anricle. 
It appears that insects possess neither 
blood-vessels nor absorbents. Cuvier has 
examined, by means of the microscope, all 
those organs in this class, which in red- 
blooded animals are most vascular, without 
discovering the least appearance of a blood- 
vessel, although extremely minute ramifi- 
cations of the tracheae are obvious in every 
part. And Lyonet has traced and deli- 
neated in the caterpillar, parts infinitely 
smaller than the chief blood-vessels must 
be, if any such existed. “ Anatomie de la 
Chenille,’’ &c. 
Yet bisects, both in their perfect, and in 
their larva state, have a membranous tube 
running along the back, in which alternate 
dilatations and contractions may be dis- 
cerned. From this circumstance it has 
been supposed to be the heart; but it is 
closed at both ends, and no vessels can be 
perceived to originate from it. 
It is obvious from these data, that the 
functions of nutrition and secretion murf 
be performed, in the animals which we are 
now considering, in a very different man- 
ner from that which obtains in the more 
perfect classes, Cuvier expresses the 
mode, in which he supposes growth and 
nutrition to be effected, by the term “ im- 
bibition.” And he explains from this cir- 
cumstance, the peculiar kind of respiration 
which insects enjoy. Since the nutritive 
fluids have not been exposed to the atmo- 
sphere, before they arrive at the parts for 
whose nourishment they are destined ; this 
exposure is eftected in the parts them- 
selves by means of tlie air-vessels, which 
ramify most minutely over the whole body. 
En un mot, le sang ne pouvant aller 
chercher fair, e’est fair, qui va chercher Ip 
sang.” 
The heart of tlie Crus tacea, according to 
Cuvier, has no auricle ; and it is what he 
calls an aortic heart. For it expels the 
blood into the arteries of the body ; and 
this fluid passes through the gills previously 
to its reaching the heart again. The diffe- 
rent parts of the system are here found 
under a mode of connection exactly the 
reverse of what we observe in fishes ; where 
the blood is sent into the gills, and passes 
subsequently into the aorta. The cireulat- 
