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 My. 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 

 il'l. 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. 



DKscRii-nox OK I'I.ATK \\.\IY. 



Fii.. i. A sagittal section of the anterior part of the neuroblast of an adult larva 

 through the root of the antennal nerve. <:, mantle layer dipping into the sub- 

 stance of the ganglion, the bourrelet intraganglionnaire of Viall a 

 superficial cells of optic ganglion ; ;/, antennal nerve ; <>', a; u-sophagus : 

 jc, rows of cells probably derived from the mantle layer ; y, large ganglion 

 cells ; -, dorsal cells of the ventral chain from which the nerves of the larva 

 arise ; y and .: are probably the functionally active parts of the neuroblast, and 

 undergo histolytic changes in the pupa. 



Fi'.. 2. A lateral section of the hemisphere of the neuroblast of the adult larva : 

 a, antennal ganglion; <; supra -n^ophageal commissure; e, mantle layer; 

 f, portion of the retinal disc;/, cells of the pyramidal ganglion; .;, -t.>mo- 

 g.i.siric ganglia ; a, central stioma of the optic ganglion ; s, optic stalk of the i-)c 

 disc. 



