556 ANTHON. [Vor. XIX. 
X. THE NERvouS TISSUE. 
The central nervous system extends along the median line 
of the ventral surface as a series of ganglia connected by 
nerve cords. The ganglia are more closely approximated in 
the anterior portion of the chain and some of the ganglia are 
united to form the brain. (Fig. 44.) Behind the brain, which 
comprises the supra-cesophageal ganglion, there is the sub- 
cesophageal ganglion and a chain of ten ganglia. Just back 
of the sub-cesophageal ganglion there are four closely approxi- 
mated ganglia. These are so closely applied that there is no 
connecting nerve cord. Posterior to these, there are six ven- 
tral ganglia which are widely separated and are joined by the 
slender ventral nerve cord. The ganglia are roughly pyra- 
midal in shape and give off four large nerve trunks; two nerve 
branches from each side and these soon divide and redivide 
into finer and finer branches. The terminal, or tenth ganglion 
(Fig. 45), is larger than the others and gives off four large 
nerve trunks from the base of the pyramid. The other ganglia 
also give off prominent nerve trunks; the one rising from the 
basal apex of the ganglion and going to the muscles of the 
body wall, while the other, which rises from the middle of the 
side of the ganglion, goes to the viscera. The muscular branch 
can easily be seen in looking at the live animal. The first 
ganglion after the thoracic group lies in the sixth segment, and 
posterior to this there is one ganglion in each segment. 
The brain proper consists of the supra-cesophageal ganglion, 
which lies above the cesophagus and is connected with the sub- 
cesophageal ganglion by the cesophageal commissures, so that 
the brain completely embraces the cesophagus. (Fig. 46.) In 
front of the brain and extending across it is the frontal gan- 
glion, which composes a part of the sympathetic system. An- 
terior to this and on either side are the optic imaginal buds. 
These are small oval swellings of the optic nerve. There are 
two other nerves given off from the supra-cesophageal gan- 
glion, one going to the antenna, the antennal branch, and the 
other running to the labium. Going out from the sub-cesopha- 
geal are three branches which connect with the mouth parts. 
