468 BERTRAM H. WATERS. 
runs out by very oblique sections separated by aslight interval 
from oblique sections of the medulla (figs. 5 and 6). The 
latter gradually lengthens, running into horizontal sections of 
the mid-brain, the extent of the latter being finally marked 
out anteriorly by the small round tubular process of the epi- 
physis, which in Amblystoma is well developed, and has con- 
siderable lumen (fig. 9, ep.). Within this area—bounded in 
front by the epiphysis, and behind by a well-marked neuro- 
mere, from which a considerable number of cells are prolife- 
rated, and which I consider the trigeminis—two fairly well 
outlined neuromeres may be seen, viz. the oculo-motor and 
trochlear. From the latter, at a high level, some cells are 
proliferated, which correspond in position at least to the roots 
of origin of the sixth nerve (see figs. 9 and 10). 
Hind -brain. 
McClure’s investigations of the hind-brain are so satisfac- 
tory that little need be added here. I have been able to 
verify his results as follows : 
(1) In the hind-brain of the Cod six neuromeres are to be 
seen, corresponding in number to those observed by him in the 
Lizard and the Chick. 
(2) In Amblystoma only five neuromeres are to be found 
in the hind-brain, the sixth or abducens being absent. 
(38) These neuromeres exhibit closely the characteristics 
already described. 
I have not been able to verify McClure’s statement that the 
vagus neuromere greatly exceeds the others in size, and I am 
inclined to think that the point will not prove constant, but 
that, as I have said, the neuromeres decrease gradually in size, 
i.e. in length, from the first to the eleventh inclusive. In 
this way only have I observed that the trigeminis exceeds the 
others of the mesencephalon. In Amblystoma, however, in 
which no abducens neuromere is apparent, the trigeminis is 
especially prominent, but I think owes its increased length to 
its fusion with the abducens neuromere, as it is about equal to 
two hind-brain neuromeres. This variation in the primitive 
