^ CLASS INSECTA. 



extend parallel to each other through the whole length of 

 the body. At intervals they have centres, from which pro- 

 length of the back part of the abdomen, and terminates anteriorly by a 

 single artery not ramified, which transports the blood into the head, 

 where it pours it out and from whence it returns into the abdomen, from 

 the very efiects of its accumulation in the head, to re-enter the heart. To 

 this the entire sanguine circulation of the insects is reduced, which have 

 thus a single artery without branches, and no veins. The alee of the 

 heart are not muscular, as Herold pretends : they are simple fibrous liga- 

 ments which keep the dorsal vessel in its place. The heart, that is to 

 say, the abdominal portion of the vessel, is divided into eight chambers 

 internally {Melolontha vulgaris), separated from each other by two conver- 

 gent valvules, which permit the- blood to proceed from behind, in front 

 of one chamber, into the other as far as the artery which conducts it to 

 the head, but which opposes its retrograde motion. Each chamber is pro- 

 vided laterally, in its anterior part, with two apertures, formed like trans- 

 verse clefts, which communicate with the abdominal cavity, and through 

 which the blood contained in this cavity can enter the heart. Each of 

 these apertures is provided internally with a small valvule in the form of a 

 semi-circle, which is attached on the aperture during the movement of the 

 systole." From this short description it is easy to conceive, that when 

 the posterior chamber is dilated, the blood contained in the abdominal 

 cavity penetrates thither by the two apertures of which we have spoken, 

 and which are named aurictclo-ventricular. When the chamber con- 

 tracts, the blood which it contains, not being able to return into the ab- 

 dominal cavity, pushes the interventricular valvule, passes into the second 

 chamber, which dilates to receive it, and which receives at the same time 

 a certain quantity of blood by the proper auriculo-ventricular apertures. 

 During the movement of the systole of this second chamber, the blood 

 passes in the same manner into the third, which equally receives some 

 by the lateral apertures; and it is thus that the blood is pushed from one 

 chamber into the other as far as the artery. It is these successive con- 

 tractions of the chambers of the heart, that one discovers through the 

 skin of the caterpillar. 



The heart of the decapode Crustacea, of squillae, limulae, spiders, &c., 

 also presents, according to the information which I have received from 

 this profound observer, similar valvules. It is enclosed in a kind of sac or 

 pericardium, which, according to him, stands in place of the auricle. These 



