i XkRrOUS SYSTEM. 



continuity of the structure in question with the mantle layer 

 renders them in the highest degree improbable. In my pre- 

 parations the continuity of this layer with the ganglion cells of 

 the pyramidal ganglion on the one hand, and with those of the 

 antennal ganglia on the other, is indubitable, audits continuity 

 with my retinal disc is no less certain. 



Of the latter Viallanes says, ' The bourrelet perilaminaire 

 should be considered as the remains of the layer of ganglio- 

 genetic cells.' The evidence on which he regards one of these 

 structures as different from the other is not very apparent, but 

 I suppose he takes such opposite views of their nature because 

 he thinks that the bourrelet intraganglionnaire is derived from 



1 1G. 66. A dingram similar to Fig. 05, at a later period. <-,, spncc between the brain 

 and head capsule ; f v cavity nf the hemisphere ; //, hemisphere ; /, leg disc ; ;/,, 

 neural crest of hemisphere ; n, neural crest of ventral ganglion ; o, optic disc ; 

 ;-, roof of the cerebral vesicle ; //, probable origin of the retinal epithelium or 

 retinal disc ; s, stomodanim ; <v, ganglion of the ventral chain. 



an invagination of the dermato-genetic layer. In this I think he 

 IKIS fallen into an error, which is due to his regarding the whole 

 of the external layer of cells as dermato-genetic, and he has 

 probably mistaken the involution of a purely nervous layer for 

 an open integumental invagination. 



Sections of the Neuroblast of the larva show that its structure 



