484 THE NERVOUS SYSTEM. 
of the brain. It will be convenient to term this layer of long 
columnar cells the mantle of the hemisphere; it disappears 
entirely during the later stages of development, and no traces 
of it remain in the adult fly. The parts of the mantle which 
remain longest are the disc covering the optic ganglion on the 
outer and inferior surface of the hemisphere and the deep 
infolding which separates its posterior from its anterior part 
(Pl. XXXIV.). The former of these I have already alluded 
to as the retinal disc; the latter certainly corresponds to the 
bourrelet intraganglionnaire of Viallanes. 
Nature and Origin of the Mantle of the Hemisphere.—Viallanes 
gives a figure of a surface-view of the embryo of Mantis 
[190, Fig. 4] in which this layer is represented in its earliest 
stage of development. It is seen to terminate in the antennal 
rudiment in front, and to cover the whole external part of the 
hemisphere. The same author gives the following description 
of the origin of the outer portion of the hemisphere, which 
he terms the first proto-cerebral lobe, in accordance with 
his nomenclature, to which attention has been directed on 
P- 442 of this work; he says: 
“We have already stated that the first proto-cerebral lobe 
consists at first of a single layer of young cells detached from 
the ectoderm by delamination. These elements, remarkable 
on account of their large size and the abundance of their proto- 
plasm, give rise indirectly to the formation of the nerve or 
ganglion cells; they will be denominated ganglio-genetic. 
DESCRIPTION OF Plate XXXIV. 
Fic. 1.—A sagittal section of the anterior part of the neuroblast of an adult larva 
through the root of the antennal nerve. e, mantle layer dipping into the sub- 
stance of the ganglion, the bourrelet intraganglionnaire of Viall 
superficial cells of optic ganglion; m, antennal nerve; @, a, cesophagus ; 
x, rows of cells probably derived from the mantle layer; y, large ganglion 
cells ; 2, dorsal cells of the ventral chain from whicl the nerves of the larva 
arise ; y and z are probably the functionally active parts of the neuroblast, and 
undergo histolytic changes in the pupa. 
Fic, 2.—A lateral section of the hemisphere of the neuroblast of the adult larva : 
a, antennal ganglion; c, supra-cesophageal commissure; e, mantle layer ; 
é, portion of the retinal disc ; f, cells of the pyramidal ganglion; g, stomo- 
gastric ganglia ; 0, central stroma of the optic ganglion ; s, optic stalk of the eye 
disc. 
