222 



CLASS III. 



INSECTA. 



Insects, which form the third class of articulated animals 

 provided with articulated legs, have, besides, a dorsal ves- 

 sel analogous to the vestige of a heart, but totally desti- 

 tute of any branch for the circulation(l). They respire by 



(1) 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 quahty, an opinion which appears to us to be fully confirmed by the admi- 

 rable researches of M. Marcel de Serres — " Memoire sur le Valsseau Dorsal des 

 Insectes" — published in the Mi-m. du Mus. d'Hist. Nat. According to the latter 

 it secretes fat, which is subsequently elaborated in the adipose tissue which sur- 

 rounds it. Lyonet says that it contains a gummy substance of an orange colour. 

 Some very recent 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 would 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 Ferussac — on a Memoir of M. [lerold on this subject, has inti- 

 mated his own opinion on the matter as deduced from his anatomical investiga- 

 tions 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 abdo- 

 men in consequence of its accumulation in the head, to again enter the heart; to 

 this all the circulation In Insects is reduced, they having merely a single artery 

 without bi-anches and no veins. The alse of the heart are not muscular as is as- 

 serted by Herold: they are mere fibrous ligaments which keep the dorsal vessel 

 in its place. The heart, that is to say the abdominal part of the vessel (in the 

 Melolontha vulgaris) is divided, internally, into eight chambers separated from 

 each other by two converging valvule which allow the transmission of the blood 

 from behind forwards, and from one chamber to another, into the artery which 



