ARTICULATA CONSIDERED AS A BRANCH. 283 



The alimentary canal of the Articulates lies in the central 

 line of the body; above it is the dorsal vessel or heart, which 

 is the principal organ of the circulatory system, arteries 

 and veins being but little developed, the blood occupying 

 all spaces not tilled by the internal organs and tissues. 



ng 



Transverse section of an Articulate animal Bee Introduced here to show the rela- 

 tive position of the alimentary canal ac ; heart or dorsal vessel dv ; and nervous gan- 

 glia ng. 



The nervous system consists of a sort of brain lying above 

 the oesophagus, from which two threads, passing around 

 the oesophagus, extend beneath the alimentary canal, along 

 the floor of the general cavity of the body, and connect at 

 certain distances small nervous centers or ganglia, whence 

 arise the nerves of the body and limbs. Each of these 

 nervous centers seems to fulfill the functions of a brain to 

 the surrounding parts, and preserves their sensibility fora 

 greater or less length of time after the animal has been 



* Figs. 354, 357-360, 363-4, 366, 383-1, 426, 442, 467, 469, 470, 472, 474, from 

 Packard's " Guide to the Study of Insects." 



