288 The Brain of the Locust. [April, 
allies, whose ears are situated in their fore legs, the first thoracic 
ganglion is a complex one. In the cockroach and in the Lefts 
(Chrysopila), a common fly, the caudal appendages bear what are 
probably olfactory organs, and as these parts are undoubtedly 
supplied from the last abdominal ganglion, this is probably com- 
posed of sensory and motor ganglia; so that we have in the 
ganglionated cord of insects a series of brains, as it were, run- 
ning from head to tail, and thus in a still stronger sense than in 
vertebrates the entire nervous system, and not the brain alone, is 
the organ of the wznd, or psychological endowments, of the 
insect. 
We will now proceed to examine the brain of the adult Ca/op- 
tenus spretus, and compare it with that of other insects; then 
study its development in the embryo, and finally examine the 
changes it undergoes in the larva and pupal stages before attain- 
ing the fully developed structure of the adult locust. 
Histological Elements of the Brain —The brain is histologically 
or structurally divided into two kinds of tissue or cellular ele- 
ments. 
1. An outer, slightly darker, usually pale-grayish white portion 
is made up of “cortical cells,” or “ ganglion cells.” (PI. 11., Fig. 
Sak te) : 
This outer loose cellular envelope of the brain consists of large 
. and small ganglion cells. Where the tissue consists of small 
ganglion cells, it is naturally from the denser arrangement of the 
smaller cells, which are packed closer together, rather darker than 
in those regions where the tissue consists of the more loosely 
disposed, large ganglion cells. 
A. The large ganglion cells (Pl. 11., Fig. 3,3 2,3 4,363% 
¢) are oval, and send off usually a shiale nerve fiber; they have 
a thin fibrous cell wall, and the contents are finely granular. The 
nucleus is very large, often one-half the diameter of the entire 
cell, and is composed of large round refractive granules, usually 
concealing the nucleolus (the granules are much larger and fewer 
in number and the nucleolus is less distinct than in the brain of 
Limulus, the king crab). These large ganglion cells are most 
abundant and largest on each side of the upper furrow, and in 
front of the “ central body,” also at the bottom of the lower fur- _ 
row, and along the exterior of the optic and antennal lobes, and 
along the commissural lobes. 
