168 
J. BEARD. 
and I think the reader will also have no difficulty in doing this 
in very many of the figures given in Pis. XVI, XVII, and 
XVIII. 
In such figures as figs. 21, 33 — 36, 49, 50, 52, one sees that 
the lips of the neural plate are very sharply defined. This 
appearance was one which struck me as remarkable in the very 
beginning of the investigations, all the more as till now no ob- 
server seemed to have noticed it, and, so far as I am aware, 
there is only one figure of it in existence, pi. xvii, fig. 12, in Pro- 
fessor His’s paper on the peripheral nervous system (No. 29). 
This figure also is taken from the spinal region of an Elasmo- 
branch embryo, and tallies almost exactly with my figs. 22 
and 32. Professor His, though he long ago noticed the ap- 
pearance, incorrectly interpreted it, and attached no particular 
importance to it. I shall refer to it again in reviewing the 
work of previous observers. 
To me it was the key to the origin of the ganglionic Anlage, 
for it showed me unmistakably that this Anlage was not, as all 
authors except His had supposed, an outgrowth of the spinal 
cord. The identification of this sharp line of division, however, 
was by no means a solution of the problem, for it was now a 
question of where the ganglionic Anlage really arises. The thin 
one-layered epiblast above the lips of the neural canal when 
contrasted with the many-layered epiblast in the region of His’s 
Zwischenstrang, suggests at once a possible point of origin ; but 
in Elasmobranchs at first no proof of this could be found, and so 
I had to look further back in earlier developmental stages before 
the neural plate is involuted. The results of this search are given 
above, and indeed it bears out my statement that this thin- 
layered epiblast above the neural lips is really the point from 
which the ganglionic Anlage has taken its origin. There is no 
need to demonstrate, by means of mathematical formulce, &c., 
that the one-layered epiblast has during the involution of the 
neural plate undergone a good deal of tension, — a tension 
which no doubt helps to separate the ganglionic Anlage on 
each side from the epiblast. 
We have now arrived at a stage such as is figured in figs. 
