THE BEAIN OF THE LOCUST. 
235 
The antennal or olfactory lobes. — Section 19. (PI. XI, Fig. 1., ant. I.) 
These are smaller than the optic lobes, though in section 19 they ap- 
pear larger. They give rise to the antennal nerve, and as the locust 
carries its ears at the base of the abdomen, the auditory nerves entering 
the third thoracic ganglion, reasoning by exclusion the antennae in 
Orthoptera must be organs of smell, and the lobes and nerves to the an- 
tennae are consequently olfactory. This is the opinion of some recent 
writers, notably Hauser. 329 The lobes are, as described by the other 
observers, filled with ball-like yellowish masses, which stain dark by osmic 
acid, much as in the commissural lobes. Nerve fibers are seen in sec- 
tion 19 to pass from one antennal lobe to the other in the rear of the cen- 
tral body and of the trabecule, while other nerve fibers are seen to pass 
into the optic lobes and the commissural lobes. This system of intra- 
lobal nerves demonstrates that there is a nervous intercommunication 
between these cerebral lobes and the ganglionic chain of the entire body. 
The commissural lobes. — From these large bodies proceed the two grea.t 
longitudinal commissural nerves, forming the connecting threads of the 
nervous cord, and which extend from the brain to the last abdominal 
ganglion, passing through the intermediate nerve centers. The lobes 
are filled with ball-like masses, of the same general appearance as in the 
antennal lobes, but more distinct and numerous. 
Comparison of the brain of the locust with that of other insects. — Newton 
rightly regards the cockroach's brain as a generalized form of brain, 
which may serve as a standard of comparison. The cockroach is geologi- 
cally one of the oldest of insects ; its external and internal structure is 
on a generalized plan, and the brain conforms to this order of things. 
Our knowledge of the cockroach's brain is derived from the photographs 
and account of Flogel, and Newton's excellent descriptions and figures, 
supplemented by two sets of sections made for us by Mr. Mason, but 
which, unfortunately, are quite defective as regards the trabecular and 
stalk of the mushroom body. The shape of the calices of the cockroach, 
as already stated, is very different from that of these bodies in the locust, 
and indeed from any other insect, the cup being very deep and the sides 
thin ; but the intimate structure seems nearly the same in the two insects. 
In the cockroach the antennal and commissural lobes are of much 
looser texture, with large and numerous ball-like masses (ballensubstanz) ; 
these are, when magnified 400 diameters, not only larger, but more dis- 
tinct from the rest of the nervous matter of the lobe than hi the locust. 
When magnified as mentioned, the ball-like masses appear to be simple 
masses of finely granular nervous matter, with darker granules, much 
like the rest of the granular portions of the brain, but with coarser 
granular masses than in the substance of the optic lobes. These ball- 
like masses are surrounded by a loose net-work of anastomosing nerve 
fibers continuous with those of the antennal nerve, and with scattered 
329 Physiologische und liistiologische Untersuchungen iiber das Geruchsorgan der Insekten. Sievold 
und Kolliker's Zeitschrift fur Wissen. Zoologie, Bd. 34, Heft. 3. 
