_1881.] The Brain of the Locust. 291 
speak, is found in the third thoracic ganglion of the locust, which 
receives the auditory nerves from the ears situated in the base of 
the abdomen; or in the first thoracic ganglion of the green grass- 
hoppers (katydids, &c.), whose ears are in their fore legs; while 
even the last abdominal ganglion in the cockroach and mole 
cricket is, so to speak, a secondary brain, since it receives sensory 
nerves from the caudal stylets which are provided with sense 
organs. 
Description of the sections of the Brain3—We will now describe 
the sections upon which the subsequent account of the brain is 
founded. The sections, unless otherwise stated, are frontal, 7. ¢., 
cut transversely across the face from before backwards ; in cutting 
thus through the head, twelve sections were made before the 
front part of the brain was touched, the thirteenth grazing the front 
of the brain. Section fourteen passed through the anterior part 
of both cadices, but did not touch the stalk of the mushroom body 
(these terms will be explained farther on). It passed through the 
central region of each hemisphere, including the front part of the 
trabecule or base of the stalk of the mushroom body. The sec- 
tion passed through the commissural lobes, the lower third being _ 
composed of the ganglion cells, but the substance of the com- 
missure itself is filled with the ball-like masses of ‘“ marksubstanz.” 
The commissures to the subcesophageal ganglion were not 
touched, and do not appear in the section, since they arise from: 
the back of the brain. 
In section 15 no additional organs are exposed. In section 16 
(Pl. u, F ig. 1) the trabecule are seen, when magnified 225 diame- 
ters, to be composed of ascending fibers, which form the base or 
origin of the double stalk of the mushroom body. ( 
Section 17 (Pl. 11, F ig. 2) is the most important of all the sec- 
tions, as the entire mushroom body and the central body are cut 
through, together with the antennal lobes, and the commissural 
lobes, and also the origin of the optic nerves. 
In section 18 (Pl. u, Fig. 4) the double nature of the stalk of 
the mushroom body is seen; the optic lobes are now well marked, 
and the razor grazed the back of the commissural lobes, as well 
as the inner side of the optic ganglion. The section passed behind 
the trabeculz and the base of the stalk and through the back of 
* We are indebted to Mr. Norman N. Mason, of Providence, R. I., for cutting and 
Mounting the sections used in making the observations here recorded. 
