232 



DR WALTER H. GASKELL. 



description of Branchipus, and Bellonci's of Spharoma ^ (c/. figs. 

 7 and 11), it would almost appear as though the cerebral part 

 of the retina in the higher forms originated from two ganglionic 

 enlargements, an external and internal enlargement, as Bellonci 

 calls them ; the external ganglion (Op. g. I., fig. 7) may be called 

 the ganglion of the retina, the cells of which form the nuclear 

 layer of the higher forms, and the internal ganglion (Op. g. II., 

 fig. 7), from which the optic nerve fibres to the brain arise, may 

 therefore be called the ganglion of the optic nerve. Bellonci 

 describes how in this latter ganghon large ganglion cells are 









ml 



?-t3;;^> •^^-^-- Lp. 



Fig. 2. — Bipolar cells of nuclear layer in retina of Brancliipus (after Claus). 

 f.hr.r., terminal fibre layer of retina ; n.l.r.r/., bipolar cells of the ganglion 

 of the retina dinner nuclear layer; vi.l., Punktsubstanz = inner molecular 

 layer ; b.m., basement membrane formed by neurilemma round central 

 nervous system. 



found very different to the small ones of the external ganglion or 

 ganglion of the retina. So also in Branchipus, judging from 

 the pictures of Berger, Claus,'-^ and from my own observations 

 {rf. fig. 11, in which the double nature of the retinal ganglion is 

 indicated), the peripheral part of the optic ganglion— ic, the 



1 ArcUv Ital. de Biol., vol. i., 1S82, p. 176. 



2 Arbeit, a. d. Znnl. Indit. Wien, Bd. vi. \k 267, 1886. 



