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 resembl e 

 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," &c., 

 in German, Leipzig, 1827, 4to. 



f See on this subject, my Memoir on the nutrition of insects, printed in 

 1799, in the M. de la Soc. d'Hist. Nat., &c. Paris, Baudouin. An. vii. 

 4to. p. 32. 



