420 W. H. GASKELL. 



munisj which is bounded in front by the lamina terminalis, 

 and is continuous behind with the third ventricle. Again^ we 

 see that here also in those parts of the walls of the cephalic 

 stomach which form the lining epithelium of these anterior 

 ventricular cavities the same marked fatty degeneration of the 

 cells has taken place as already mentioned in the region of 

 the infra-oesophageal ganglia. 



This figure is much the same as fig. 1, PI. II, in Edinger's 

 paper (18) on the " Comparative Anatomy of the Brain," in 

 which he shows that the simple cerebrum of Ammocoetes cor- 

 responds to the olfactory lobes and corpus striatum of the higher 

 Vertebrates. In this most instructive paper he points out that 

 the cortical grey matter of the brain does not appear until we 

 reach the reptiles. In fishes, as in Ammocoetes, the cerebral 

 hemispheres consist simply of an olfactory part, and the basal 

 ganglion or corpus striatum, with the grey matter inside and 

 the white matter outside. The peripheral cortex of grey 

 matter is only formed much later in phylogenetic development. 

 The connecting commissure between the two basal ganglia is 

 described by Ahlborn as the anterior commissure, and it is 

 recognised as such by Edinger through the whole ascending 

 series of Vertebrata. If, then, the olfactory lobes and basal 

 ganglia are the cerebral portion of the supra-CESophageal 

 ganglia, then the anterior commissure is the commissure 

 which originally connected together the corresponding parts of 

 the supra-oesophageal ganglia; and as evidence of its antiquity 

 we see that it is stated to be the earliest formed of all the 

 commissures of the brain. 



Further, we see that these two nervous masses which form 

 the brain proper and the olfactory lobes are not only in the 

 position of the supra-oesophageal ganglia with respect to the 

 walls of the cephalic stomach, but also are in connection with 

 a special optic portion which is also supra-oesophageal in situa- 

 tion, and gives origin to eyes of a strictly Arthropodan type. 



Lying between and dorsal to the two cerebral lobes we see 

 in fig. 1 the large rounded right ganglion habenulse ; much 

 less conspicuous is the smaller left ganglion habenulae. These 



