[34] Our knowledge of the development of Acipenser is in the main derived from Salensky’s valuable observations. His full memoir is unfortunately published in Russian, and I have been obliged to satisfy myself with the abstract (No. [90]), and with what could be gathered from his plates. Prof. Salensky very kindly supplied me with some embryos; and I have therefore been able to some extent to work over the subject myself. This is more especially true for the stages after hatching. The embryos of the earlier stages were not sufficiently well preserved for me to observe more than the external features and a few points with reference to the formation of the layers.
[35] Seven micropylar apertures, six of which form a circle round the seventh, are stated by Kowalevsky, Wagner, and Owsjannikoff (No. [89]) to be present at one of the poles of the inner egg membrane. They are stated by Salensky to vary in number from five to thirteen.
[36] Salensky believes that the notochord is derived from the mesoblast. I could not satisfy myself on this point.
[37] If these identifications are correct the barbels of fishes must be phylogenetically derived from the papillæ of a suctorial disc adjoining the mouth.
[38] Alexander Agassiz was fortunate enough to succeed in procuring and rearing a batch of eggs of this interesting form. He has given an adequate account of the external characters of the post-embryonic stages, and very liberally placed his preserved material of the stages both before and after hatching at Prof. W. K. Parker’s and my disposal. The account of the stages prior to hatching is the result of investigations carried on by Professor Parker’s son, Mr W. N. Parker, and myself on the material supplied to us by Agassiz. This material was not very satisfactorily preserved, but I trust that our results are not without some interest.
[39] I have as yet been unable to make out these structures in section.
[40] These papillæ are very probably sensitive structures; but I have not yet investigated their histological characters.
[41] Vide Steindachner, Polypterus Lapradei, &c., and Hyrtl, “Ueber d. Blutgefässe, &c.” Sitz. Wiener Akad., Vol. LX.