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-esoplmgial 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, and 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 of 
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 
the organs of generation. When ganglia do not exist 
