176 
J. BEARD. 
If in such stages it is difficult in the trunk to be always 
quite certain of the sharp boundary line separating the gan- 
glionic Anlagen from the closing neural plate, such is never the 
case in the head. I cannot remember having seen a single Elas- 
mobranch section in which for the head it was at all a difficult 
matter to distinguish the limits of the two; and in spite of 
this fact there are no figures in existence which show this 
separation such as I depict it in figs. 44 — 48, 24 — 27, 29. 
Here, as in the trunk, the position of the ganglionic Anlagen 
between the lips of the neural tube (figs. 25, 44, 47) prevents 
their complete closure. But soon the Anlagen begins to grow 
downwards and outwards towards the lateral surface of the 
body. This outward growth leads, as is well known from the 
researches of recent years, to a difference in position between 
the ganglia of the head and those of the trunk. For while 
the latter lie between the muscle-plates and the spinal cord, 
the former take up a position outside the mesobiast and close 
to the skin. 
The portion of the ganglionic Anlagen of the head derived 
from the neural epiblast corresponds, in development at least, 
with the Anlagen of the spinal ganglia, but the cranial ganglia 
of (apparently) all Vertebrates acquire a further form-element 
derived from the lateral epiblast above the gill-clefts, and at 
about the level of the notochord. For the formation of this 
element I have not in this paper given any figures, but I 
think such figures can be here entirely dispensed with, seeing 
that in a former paper (No. 6) treating of the branchial sense 
organs and their ganglia I figured a great many stages of this 
ganglionic formation, for, what I there called the branchial 
ganglia make up this additional form-element of which I just 
wrote. I believe I showed conclusively enough in that paper 
that above the gill-cleft ganglionic elements were given off 
into the main ganglion — indeed, it then seemed to me that 
most, if not all, the ganglion was formed there. As even such 
a severe critic as Professor Gegenbaur expresses himself 
satisfied that such form-elements of the ganglion take their 
origin above the gill-cleft, I may assume it to be unnecessary 
