[201] Grundriss d. Vergleichenden Anat. p. 494.
[202] Loc. cit.
[203] No attempt has been made to describe in detail the different appearances presented by the protovertebræ in the various parts of the body, but in each stage a protovertebra from the dorsal region is taken as typical.
[204] Zeitschrift f. Anat. Entwicklungsgeschichte, Vol. 1.
[205] Hensen loc. cit.
[206] For the history of protovertebræ and muscle-plates in Birds, vide Elements of Embryology, Foster and Balfour. The statement there made that the horizontal splitting of the mesoblast does not extend to the summit of the vertebral plate, must however be regarded as doubtful.
[207] Vide Elements of Embryology, p. 56.
[208] Dr Götte, Entwicklungsgeschichte der Unke, p. 534, gives a different account of the development of the protovertebræ from that in the text. He states that the muscle-plates do not give rise to the main dorso-lateral muscles, but only to some superficial ventral muscles, while the dorso-lateral muscles are according to him formed from part of the kernel of the protovertebræ internal to the muscle-plates. The account given in the text is the result of my own investigations, and accords precisely with the recent statements of Professor Kölliker, Entwicklungsgeschichte, 1876.
[209] The type of development of the muscle-plates of Amphibians would become identical with that of Elasmobranchii if their first-formed mass of muscle corresponded with the early-formed muscles of Elasmobranchii, and the remaining cells of both layers of the protovertebræ became in the course of development converted into muscle-cells indistinguishable from those formed at first. Is it possible that, owing to the distinctness of the first-formed mass of muscle, Dr Götte can have overlooked the fact that its subsequent growth is carried on at the expense of the adjacent cells of the somatic layer?
[210] Ehrlich, “Ueber den peripher. Theil d. Urwirbel.” Archiv f. Mic. Anat. Vol. XI.