THE 



ANIMAL KINGDOM. 



THIRD CLASS OF ARTICULATED ANIMALS, 



AND PROVIDED WITH ARTICULATED FEET. 



The insects (INSECTA) 



have articulated feet, a dorsal vessel, which holds the si- 

 tuation of every vestige of heart, but without any branch for 

 circulation ;* respire through two principal tracheae, which 



* Anatomists are greatly divided with regard to this organ. Many con- 

 sider it as a genuine heart; others (and such is the opinion of M. Cuvier, 

 and one which appears to us to have been fully confirmed by the satisfac- 

 tory researches of M. Marcel de Serres\ entirely deny this position. 

 According to the last mentioned author, the function of this vessel is the 

 secretion of fat, which is afterwards elaborated in the adipose tissue which 

 envelopes it. Lyonet says that it encloses a gummy substance of an 

 orange colour. Some very recent observations appear to establish the 

 existence of a few small vessels ; but, besides that this circulation would 

 be very partial, the insects must always differ greatly in this respect from 

 the Crustacea, in as much as the blood does not return to the heart. M. 

 Straus, in reviewing a memoir of M. de Herold on the subject in the 

 " Bulletin Universel," has given us his own opinion, founded on his own 

 researches, on the Melolotitha. " The dorsal vessel," he says, " is the 

 true heart of the insect, being, as in the superior animals, the locomotive 

 organ of the blood, which, instead of being contained in vessels, is spread 

 through the general cavity of the body. This heart occupies the entire 



VOL. XIV. B 



