MOEPHOLOGICAL STUDIES. 
193 
should have anticipated that a difference of opinion was im- 
possible, had it not been for the fact that His and Kolliker, 
following Remak and the older embryologists, absolutely deny 
the fact. I feel quite sure that no one studying the develop- 
ment of the nerves in Elasmobranchii with well-preserved 
specimens could for a moment be doubtful on this point. And 
I can only explain His’s denial on the supposition that his 
specimens were utterly unsuited to the investigation of the 
nerves. I do not propose in this work entering into the histo- 
genesis of nerves, but may say that for the earlier stages of 
their growth, at any rate, my observations have led me in 
many respects to the same results as Gotte (‘Entwickl. d. 
Unke/ pp. 482 — 483), except that I hold that adequate proof 
is supplied by my investigations to demonstrate that the nerves 
are for their whole length originally formed as outgrowths of 
the central nervous system. As the nerve-fibres become differ- 
entiated from the primitive spindle-shaped cells, the nuclei 
become relatively more sparse, and this fact has probably 
misled Kolliker. Lowe, while admitting the existence of 
nuclei in the nerves, states that they belong to mesoblastic 
cells which have wandered into the nerves. This is a purely 
gratuitous assumption, not supported by observation of the 
development.” 
I could have been content to leave this matter of the anterior 
roots unnoticed but for two circumstances. In the first place 
the figures which Balfour has given of their development in 
the ‘ Comparative Embryology ’ (vol. ii, p. 371, fig. 267), 
“Elasmobranch Fishes” (PI. X, fig. 7), and in the paper on the 
spinal nerves (No. 1, PI. XYI, figs. Da. b. and c. PI. XVII, 
figs. H ii, Iu, and E. b.) are very diagrammatic, and His would 
be justified from his standpoint in objecting to their repre- 
senting the true facts. On the other hand, I can raise the 
same objection to the diagrammatic figure of the development 
of anterior roots iu Pristiurus, which His represents on p. 393 
(No. 34, fig. 1) of his recent work. Nay, I cannot help insisting 
that if Balfour’s figures were not what one might expect, His’s 
figure is incorrect to a far greater degree, and the “Ehreu- 
