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J. BEAKD. 
notochord is already partly separated off) the neural plate 
is a broad, slightly-grooved, shallow structure, which presents 
no appearance of differentiation. Very soon the invagination 
process begins, and with it the Aulagen of the spinal ganglia 
begin at once to be distinguishable from the rest of the neural 
plate. At the extreme outer boundary of what is really the 
“Anlage” of the spinal cord a commencing proliferation of 
the deeper layers of the epiblast is observable (fig. 2). This 
leads to the appearance of a bud-like outgrowth of cells at each 
side of the spinal cord Anlage. On the one hand this out- 
growth is very soon sharply distinguishable from the spinal 
cord Anlage ; on the other hand, it begins to separate some- 
what from the rest of the epiblast in the form of a somewhat 
wedge-shaped mass of cells. In figs. 3, 5, 9, this process is 
readily made out. From an inspection of these figures it will 
be obvious that the whole thickness of the epiblast is not con- 
cerned in this outgrowth. The outer layer of epiblast 
is quite indifferent, and neither takes share in the 
Anlage, nor presents any resemblance at all to a 
sense epithelium, a point on which I shall have more 
to say in connection with Dr. Eisig’s comparisons. 
The epiblast in the region of the ganglionic Anlage, and for 
some distance lateral of this, is composed of several cell layers 
(fig. 1). Now, the way in which the ganglionic Anlage sepa- 
rates from the rest of the epiblast is such that a triangular 
wedge of epiblast is left as the limit of the ganglionic forma- 
tion. The poiut of this wedge, which exists in much the same 
form for a considerably later period of development, projects 
towards the mesoblast. It is somewhat difficult to describe 
these appearances in words ; a glance at figs. 2, 14, 38 suffice, 
I think, to make clear the meaning of the Zwischenstrang of 
His, for that is what this portion of indifferent epiblast really 
is. Let us follow the lateral epiblast upwards from the side 
of the trunk to the lips of the neural plate. At first it is for 
some distance neuralwards only one layer thick ; soon this 
changes, and it becomes gradually thicker ; and if we follow it 
in such a section as is figured in figs. 14, 38, we see that at 
