374 The Brain of the Embryo and Young Locust. [ May, 
the central body and the two mushroom bodies. The stratum of 
cortical ganglionic cells is, at this period, quite distinct from the 
paler unstained granular brain matter. The ganglionic cell-por- 
tion gradually passes into the central white brain substance, 
which is composed of fine granules or nuclei alone, and which do 
not apparently differ from the granules scattered among the 
ganglion cells. It is to be observed that there are no fibers 
among the granules. It thus appears that the brain of insects, 
like the other ganglia, originally consists of a paler portion formed 
of fine clear granules (nuclei ?), enveloped by a thick, irregular 
layer of nucleated cells, containing fine granules outside of the 
nucleus. 
As the fibers of the adult brain are evidently secondary pro- 
ducts, it would appear that they must be transformed granules or 
nuclei, and not in all cases, at least, the fibers thrown off from 
the ganglion cells, although at this time the ganglion cells have 
no fibers, the fibers of those seen in the adult brain being also 
secondary growths. It may be that the white inner granulo- 
fibrous matter of the adult brain is (1) made up of modified gran- ~ 
ules, which in some cases remain such, and in others form fibers, 
and (2) of fibers sent in from the cortical ganglion cells. 
Comparison of the Brain at this Stage with the first Thorac 
Ganglion.—If we compare at this stage of development of the 
nervous system the brain with one of the ganglia of the trunk, 
we shall obtain a fair idea of the primitive difference between the 
brain and one of the ordinary ganglia. By a glance at the figures 
of the two it will be seen that the organization of the thoracic 
ganglion is essentially simple. It is divided into two portions oF 
regions. The central granular region is enveloped by a thick 
stratum of cortical ganglion cells. The whole ganglion in section 
is rudely hour-glass-shaped and much smaller than the brain 
There is no differentiation into distinct lobes as in the brain. 
The formation of the brain, as is well known by embryologists, is 
one of the earliest steps in the development of the nervous syS~ 
tem, the entire system being at an early date in the life of the 
embryo set apart from the epidermis or integument, the latter 
with the nervous system originating from the ectoderm or outer 
germ-layer. 
Second Embryonic Stage, B—In embryos more advanced, and 
just ready to hatch, the eyes being now dark red, the cen 
