466 BERTRAM H. WATERS. 
convinced, however, that an osmic acid, or some other more 
distinctive paeparation, would show each of these neuromeres 
to be connected with a nerve-root. In regard to the segmental 
value of the two nerves of this region Gaskell (9) has said, 
“Both these nerves possess within themselves structures 
which appear to me to have been originally the nerve-cells 
and nerve-fibres corresponding to the cells and nerve-fibres of 
the stationary ganglion on the posterior root of a spinal 
nerve; so that in the possession of afferent fibres with a sta- 
tionary ganglion, as well as in the possession of efferent fibres, 
these two nerves conform each to the type of a segmental 
nerve.” Kupffer, in a recent paper (16, 0), speaks of a short 
fibrillar cord which springs from the ventral aspect of the 
mid-brain ; also of a cord springing dorsally from the mid- 
brain, of the position of which as an eye muscle-nerve he is in 
doubt. Should it prove to be constant he would assign it to 
the branchial system, thus establishing its primitive character. 
The existence of such nerve-elements in connection with what 
must uow be granted to be segmental structures seems at last 
to define the position of these nerves, in explanation of which 
so many different opinions have been held. 
The results obtained from the preparations of Ambly- 
stoma are offered mainly in confirmation of those already 
stated. They are more satisfactory as regards the enumera- 
tion and location of neuromeres, less so as to the nerve origins, 
the stages being so young that the latter are indefinite, and 
their determination much obstructed by the abundance of 
yolk spherules. While it has been said that the neuromeric 
segmentation seems to be retarded, this must be understood 
as being only relatively true, and, as degeneration of the seg- 
ments begins with the most anterior, early stages were neces- 
sary. The figures show a series taken as nearly as possible in 
a horizontal plane through the mid-brain shortly after the 
closing in of the medullary folds, the section at the lowest 
level showing, in slightly oblique section, the fore-brain, the 
obliquity being due to a slight amount of cranial flexure. 
Anteriorly is seen the first or olfactory neuromere with the 
