176 ANATOMY AND PHYSIOLOGY 



optic nerves, which are the largest in the whole body, 

 the most considerable are the lateral cords uniting 

 the two ganglia in question ; their length is in pro- 

 portion to the diameter of the esophagus, and as that 

 is least in sucking insects, the two ganglia in these 

 approximate almost to touching, but they are remote 

 in gnawing species, and the uniting nerves are pro- 

 portionately elongated. 



The sub-esophagial ganglion (the cerebellum of 

 Burmeister, or rather what is called the medulla ob- 

 longa by Mr. Newport, who regards the true ana- 

 logue of the cerebellum to be entirely wanting in 

 insects,) is commonly heart-shaped, or inclining to 

 transversal, and lies at the base of the cavity of the 

 skull. Anteriorly it gives birth to several nervous 

 stems on each side, which supply branches to the 

 mandibles, maxillae, labium, tind the neighbouring 

 muscles ; and, posteriorly, it gives origin to the long 

 nerves which form the ventral chain. 



The latter is composed of either one or two equal 

 nervous cords, and the maximum of ganglia which it 

 contains is eleven, in which case one is allotted to each 

 segment. Frequently, however, they are concentrated 

 in the thorax, and the abdomen entirely deprived oi 

 them. The mode of their distribution is most regular 

 in larvae. Each of them sends off nervous filaments, 

 commonly amounting to three pair on each side; those 

 in the thorax supply the wings and legs, those of the 

 abdomen the muscles with which its cavity is furnished, 

 and the hinder abdominal one transmits branches to 

 tfie organs of generation. When ganglia do not exis; 



