ARTICULATED ANIMALS. 5 
■ 
* 
ceive the air through stigmata, pierced on the sides, and dis- 
tribute it, by infinite ramifications, into all parts of the body. 
There is but a vestige of a heart, which is a vessel attached 
along the back ; it undergoes alternate contraction, but no 
branches to it have been discovered, so that we must believe 
that the nutrition of the parts takes place by imbibition. It 
is probably this sort of nutrition which has necessitated the 
sort of respiration proper to insects, because the nutritive 
fluid not being contained in vessels % and not capable of being 
directed to circumscribed pulmonary organs, in search of air, 
it was necessary that the air should be spread through the 
whole body, to reach the fluid. This is also the reason why 
insects have no secretory glands, but only long spongy vessels, 
which appear to absorb, by their great surface, in the 
mass of nutritive fluid, the proper juices which they should 
produce f. 
The insects vary infinitely in the forms of their organs of 
the mouth and of digestion, as well as in their industry and 
mode of living. Their sexes are always separate. 
The Crustacea and arachnida were for a long time united 
with the insects under one common name, and they resemble 
them in many respects, both in external form, and in" the dis- 
position of the organs of motion, of sensation, and even of 
manducation. 
* M. Cams has recognized some regular movements in the fluid which 
fills the body of the larvae of certain insects ; but these movements do not 
take place in a close system of vessels, as in the superior animals. See his 
treatise, intitled, " Discovery of a Simple Circulation of the Blood/ 5 &c., 
in German, Leipzig, 1827, 4to. 
f See on this subject, my Memoir on the nutrition of insects, printed in 
1/99, in the M. de la Soc. d’Hist. Nat., &c. Paris, Baudouin. An. vii. 
4 to. p. 32. 
