1881. ] The Brain of the Locust. 287 
the insect consists of a chain of ganglia connected by nerves or 
commissures, while the spinal cord of the fish or man is essen- 
tially ““a double and fused series of nerve-centers.’ Moreover, 
. if the vertebrate cord is cut through, a section shows that it con- 
sists of two kinds of substances or tissues, called the “ gray” and 
“white” substance. The gray matter is situated in the center, 
and consists largely of nerve or so-called “ ganglion cells,” while 
the external white matter of the brain or cord is composed of a 
mass of nerve fibers. Now, in the nervous system of insects 
there is nothing to compare with these substances, but the ganglia, 
on the contrary, as we shall see farther on, consist primarily of 
an external layer of ganglion cells, whose fibers pass in to form a 
central fibrous mass or net-work, the meshes of which are filled 
with a fine granulated nerve substance, the nature of which is 
not clearly understood. Moreover, the entire brain of an insect 
is white, as are all the ganglia. 
A ganglion in its simplest form isa little rounded mass, or 
nodule, of ganglion cells, with fibers leading from them: such 
cells are represented by Fig. 3a—3e, on Plate 11. Now when the 
fibers lead in from the sensitive hairs on the crest of the insect, 
or from the antennz, or the eyes or ears, and end in separate 
masses or lobes, which are modified ganglia, such ganglia are 
regarded as ‘‘ sensory ganglia,” and the nerves leading in from 
them are called ingoing or “afferent nerves,” while the ganglia 
which give rise to the outgoing or “efferent” nerves, 7. e., those 
going to the muscles of the wings, legs, &c., are called “ motor 
ganglia.” 
It should be borne in mind as the result of recent studies by 
several observers, as Leydig, Flogel, Dietl and Newton, that the 
subcesophageal ganglion, or “ brain,” of the insect is much more 
complex than any other ganglion, consisting more exclusively both 
of sensory as well as motor ganglia and their nerves. But it should 
also be understood that the subcesophageal ganglion also receives 
nerves of special sense, situated possibly on the palpi, and possibly 
on the tongue, at least the latter is the case with the bee; hence, 
this ganglion is probably complex, consisting of sensory and motor 
ganglia. The third thoracic ganglion is also, without doubt, a 
complex one, as in the locusts the auditory nerves pass into it 
from the ears, which are situated at the base of the abdomen. 
But in the green grasshoppers, such as the katydids | and their 
