192 
J. BEAltD. 
trigeminus ganglia, but there can be little doubt that they also 
exist for these at some stage or other. 
After the fusion of the mass of each cranial ganglion with 
the skin, form-elements are, as we have seen, given off into it. 
The ganglion leaves the skin, aud, as in Sharks, almost certainly 
leaves sensory nerve branches behind it. The sense-organ 
rudiments afterwards disappear. I have not followed the steps 
of this process in the Chick, but I cannot doubt the general 
accuracy of Kastschenko’s account (No. 40, pp. 281 — 284), for 
it agrees fairly well with Professor Froriep's earlier researches 
(No. 17) on the fate of the rudiments in Mammals. 
This finishes the general account of the first formation of 
cranial ganglia in the Chick. 
III. The Development of the Anterior Roots of 
Spinal Nerves in Elasmobranchs. 
In Balfour's account of the spinal nerves in Elasmobranchii 
(Nos. 1 and 2), he described the anterior roots as direct cellular 
outgrowths from the lateral ventral region of the spinal cord, 
and in the second volume of the ‘ Comparative Embryology/ 
p. 372, he says : “ The anterior roots of the spinal nerves 
appear somewhat later than the posterior roots, but while the 
latter are still quite small each of them arises as a small 
but distinct concise outgrowth from the ventral corner of the 
spinal cord, before the latter has acquired its covering of white 
matter. From the very first the rudiments of the anterior 
roots have a somewhat fibrous appearance and an indefinite 
form of peripheral termination, while the protoplasm of which 
they are composed becomes attenuated towards its end. They 
differ from the posterior roots in never shifting their point of 
attachment to the spinal cord, in not being united to each 
other by a commissure, aud in never developing a ganglion. 5 ' 
The anterior roots grow rapidly, aud soon form elongated 
cords of spindle-shaped cells with wide attachments to the 
spinal cord." And in a note at the foot of p. 372 : “ The 
cellular structure of embryonic nerves is a point on which I 
