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 smaller 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 c . 
This opinion receives additional confirmation from the 
mode in which respiration is performed in insects. In 
a Lyonet Anat. 427—- b Cuv. Anal. Corny, iv. 418—. 
c Mem. du Mas. 1811). 71. 
