INTERNAL ANATOMY OF INSECTS. 87 
Lyonnet, whose piercing eye and skilful hand traced the 
course of so many hundred nerves and bronchie long 
after they became invisible to the unassisted eye, and 
which were a thousand times smaller than the princi- 
pal 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 commu- 
nicating with it?. And Cuvier, whose unrivalled skill 
in Comparative Anatomy peculiarly 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 conclusion, that insects have no 
circulation, that their dorsal vessel is no heart, and there- 
fore ought not to be called by that name: that it is ra- 
ther a secretory vessel, like many others of that kind in 
those animals. As to the nature of the fluid that it se- 
cretes, and its use, he thinks it impossible, from our present 
information on the subject, to form any satisfactory con- 
clusion, Marcel de Serres informs us—which further 
proves 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 further confirma- 
tion from the mode in which respiration is performed in 
insects. In those animals that have a circulation, this 
takes place by means of Jungs or gills ;—thus we find, even 
* Lyonnet Anat. 427—. > Cuv. Anat. Comp. iv. 418—. 
¢ Mem. du Mus. 1819. 71. 
