230 REPORT UNITED STATES ENTOMOLOGICAL COMMISSION'. 
optic ganglia were cut through hy the microtome, affording instructive 
sections of the three lenticular masses of white unstained granulo-fibrous 
substance surrounded by ganglion cells. 
INTERNAL TOPOGRAPHY OF THE BRAIN. 
Disregarding the envelope of cortical ganglionic cells, though they are 
evidently of primary importance in the physiology of the insect's brain, 
we will now describe the internal topography of the brain. It consists 
primarily of an irregular net-work of nerve-fibers, inclosing masses of 
granulated nerve matter. This mass is divided into a number of sep- 
arate areas or lobes, of which the ''central body" (corpus centralc of 
Flogcl and Newton) is single and situated between or in the median line 
of the two hemispheres. There is also a primitive superior and inferior 
central region, better shown, however, in the brain of the embryo and 
larval locust than in the adult. Besides these areas are the rounded 
masses or "lobes," i. e., the optic, antennal, or olfactory and commissural 
lobes; the optic nerves arising from the optic lobes, the antennal nerves 
from the antennal lobes, and the commissures surrounding the oesopha- 
gus and connecting the brain with the subcesophageal ganglion ; these 
arise from the commissural lobes. Finally a "mushroom body" is 
situated in the upper and central part of each hemisphere. 
The central body. — This is the only single or unpaired organ in the 
brain. It is best seen iu section 17 (PI. X, Fig. 2), which also passes 
through the optic and antennal lobes and the trabecular and mushroom 
bodies. This singular orgau is apparently present in all winged insects, 
though differing somewhat/ in structure in different insects. It is, as 
seen in PI. X, Fig. 2, situated iu the same plane as the peduncle and 
in the same plane as the center of the entire mushroom body, and rests 
upon the inner sides of the trabecular. Section 1G does not pass through 
it, though the next section, which is - 5 1q incli thick, passes through its 
middle. Section 18 (Fig. 4) passes through its back, while the next sec- 
tion does not include any part of it ; hence its antero posterior diameter 
is slightly over of an inch. It is about twice as broad as high, and 
thus is a small body, though from the universality of its occurrence in 
winged insects, it may be one of considerable importance. 
It is surrounded by a dense net- work of fibers containing a few small 
ganglionic cells, the fibres in front continuous with those near the bottom 
of the frontal median furrow and connecting the two optic lobes. Pos- 
teriorly the fibers apparently are not continuous with those of the trabe- 
cular; hence the central body appears to be quite isolated from the rest 
of the brain. Its substance, when magnified 400 diameters, appears to 
be a white granular matter like the adjoining parts of the brai^. It is 
divided into two parts, the superior and inferior, the former part con- 
stituting the larger part of the body. The inferior portion is separated 
by fibers from the superior; it contains numerous nucleated spherical 
cells situated either irregularly or perhaps primarily (see PI. XIV, Fig. 3, 
