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HENRY ORE. 
them. In the embi’yo of fig. 22 the optic outgrowths are bent 
backwards and upwards, and in the embryo of fig. 23 the eye 
has progressed so far that the lens has appeared. 
In the Amblystoma embryo of series d, in which the fore- 
brain is not yet enclosed, there is no trace of the optic vesicles. 
The next older stage of Amblystoma among my specimens is 
illustrated in figs. 12 e — 16 f. The condition of the cranial 
flexure is shown at 12 e. In the anterior wall of the brain 
may be seen the optic groove (o. g.), and behind the latter is 
the anterior fold (A. F.). Immediately posterior to the anterior 
fold is the rudiment of the infundibulum. At this stage the 
primary triple division of the brain is not yet very pronounced, 
and there is no trace of nerve-fibres in the brain. The position 
of the rudiment of the epiphysis ( Eph ., fig. 13 e) indicates the 
posterior extent of the primary fore-brain. In fig. 16 f the 
fore-brain is represented in section parallel to its morphologi- 
cally anterior surface very near the latter, and in the region of 
the optic stalks {Eg.). In this section the lateral thickenings 
of the brain wall in front of the optic stalks are the rudiments 
of the corpora striata, which appear much earlier in Amblystoma 
than in the Lizard. Fig. 15 f represents a horizontal section 
of the embryo passing through the dorsal part of the pharyngeal 
cavity and through the mid-brain above the region of the in- 
fundibulum. This section shows the rudiments of the eyes 
(-By.), which as yet possess no lens. Fig. 14 p represents a 
horizontal section through the hind-brain and dorsal medulla. 
This section shows the rudiments of the fifth, seventh and 
eighth, ninth and tenth cranial nerves. In three places the 
hind-brain shows a marked dilation of its lumen, and the 
lateral walls of the brain pass around these dilated parts un- 
diminished in thickness. Opposite these dilated parts of the 
lumen arise the three chief nerve-roots of the hind-brain. The 
most anterior dilation corresponds to the fifth nerve- root (n. V ). 
The next dilation corresponds to the common root of the seventh 
and eighth nerves [n. VIII and VII), and the posterior dilation 
corresponds to the root of the tenth nerve {n. X). The rudi- 
ment of the ear (B.) lies between the regions of the posterior 
