184 
J. BEARD. 
blastic somite on the right — and here it is difficult to distinguish 
a ganglionic Anlage — but on the left it has cut the segment 
near its end and the ganglionic Anlagen is distinctly seen at 
g. a. as a small plug of cells being cut out of the epiblast just 
outside of the neural plate. 
The fourth section (fig. 73) shows very distinctly on both 
side the spinal ganglionic Anlagen (g. a.). The boundaries of the 
infolding spinal cord are sharply marked off at o from the gan- 
glionic Anlagen, which lies just outside them at g.a. This figure 
shows that the spinal ganglia in the Chick take their origin 
in exactly the same way as those of Elasmobranchii, and that 
by the cutting out of the ganglionic Anlagen at g. the epiblast 
to the outer sides of them is left as a somewhat triangular body, 
which, as in Sharks, where it is not so distinct, represents the 
“ Zwischenstrang” of His. The following three figures, taken 
still farther forwards from the embryo, show the same appear- 
ances even better. On examining, for example, the six figures 
(fig. 75, 76, 80, 81, 85, 89), one sees the following things: — The 
spinal cord is rapidly closing in, and its lips are sharply defined 
from the ganglionic Anlagen ( g . a.) just outside them. With 
the lateral epiblast (<?.) the Anlagen of the ganglia have lost all 
connection, and only retain it with the epiblast at the re-entering 
angle between spinal cord and skin. The epiblast at ie, of which 
the Anlagen, as in figs. 70, 71, originally formed a part, is, ever 
since the separation, only composed of a single layer of cells, 
which, in consequence of the tensions arising in connection with 
the infolding process, has become much lengthened. Outside 
this thin-layered part the epiblast passes almost abruptly 
into a much thicker-layered portion of the outer layer, which 
has taken no share at all in the formation of the ganglia. 
This thicker portion (fig. 68) forms a somewhat triangular 
mass of cells, the apex of which is directed towards the meso- 
blast. From a consideration of these figures (figs. 75, 76, 80, 
81, 85, 89,), and of several other figures (figs. 98, 99, 102), 
to be afterwards noticed more in detail, the conclusion is forced 
upon any unbiassed observer that the triangular mass of cells 
is identical with the so-called “ Zwischenstrang” of llis. The 
