[55] [May 18, 1876.—Since the above was written Hensen has succeeded in shewing that in mammals the rudiments of the posterior roots arise in a manner closely resembling that described in the present paper; and I have myself, within the last few days, made observations which incline me to believe that the same holds good for the chick. My observations are as yet very incomplete.]
[56] [May 18, 1876.—Hensen's observations, as well as those recently made by myself on the chick, render it almost certain that the nerves in all Vertebrates spring from the spinal cord.]
[57] Balfour, “A Preliminary Account of the Development of Elasmobranch Fishes,” Q. J. Micros. Sc. 1874, plate XV. fig. 14, v.g. [This edition, Pl. 4, fig. 14, vg].
[58] The nervous cords of other Annelids resemble that of Lumbricus in the relations of the ganglion-cells of the nerve-fibres.
[59] Tafeln zur vergleichenden Anatomie, Taf. iii. fig. 8.
[60] The figures on these Plates give a fair general idea of the appearance presented by the developing spinal nerves; but the finer details of the original drawings have in several cases become lost in the process of copying.
The figures which are tinted represent sections of embryos hardened in osmic acid; those without colour sections of embryos hardened in chromic acid.
IX. On the Spinal Nerves of Amphioxus[61].
During a short visit to Naples in January last, I was enabled, through the kindness of Dr Dohrn, to make some observations on the spinal nerves of Amphioxus. These were commenced solely with the view of confirming the statements of Stieda on the anatomy of the spinal nerves, which, if correct, appeared to me to be of interest in connection with the observations I had made that, in Elasmobranchii, the anterior and posterior roots arise alternately and not in the same vertical plane. I have been led to conclusions on many points entirely opposed to those of Stieda, but, before recording these, I shall proceed briefly to state his results, and to examine how far they have been corroborated by subsequent observers.