88 INTERNAL ANATOMY OF INSECTS. 



sive, those which may be urged for the more modern opi- 

 nion that no circulation exists in insects, properly so 

 called, appear to have still greater weight. Lyonet, 

 whose piercing eye and skilful hand traced the course of 

 so many hundred nerves and bronchia long after they 

 became invisible to the unassisted eye, and which were 

 a thousand times smallet than the principal blood-vessels, 

 opening into so large an organ as the supposed heart of 

 insects, might be expected to be, could never discover 

 any thing like them. His most painful researches, and 

 repeated attempts to inject them with coloured liquors, 

 were unable to detect the most minute opening in the 

 dorsal vessel, or the slightest trace of any artery or vein 

 proceeding from or communicating with it a . And Cuvier, 

 whose unrivalled skill in Comparative Anatomy peculi- 

 arly qualified him for the investigation, repeated these 

 inquiries, and tried all the known modes of injection, 

 with equal want of success ; and is thus led to the con- 

 clusion, that insects have no circulation, that their dorsal 

 vessel is no heart, and therefore ought not to be called 

 by that name : that it is rather a secretory vessel, like 

 many others of that kind in those animals. As to the 

 nature of the fluid that it secretes, and its use, he thinks 

 it impossible, from our present information on the subject, 

 to form any satisfactory conclusion b . Marcel de Serres 

 informs us which further seems to prove that it can be 

 no real heart that this vessel may be totally removed 

 without causing the immediate death of the insect . 

 This opinion receives additional confirmation from the 

 mode in which respiration is performed in insects. In 



3 Lyonet Anat. 427. b Cuv. Anat. Comp. iv. 418, 



c Mem. du Mus. 1819. 71. 



