[363] The numbers appended to authors' names refer to the list of publications at the end of the paper.
[364] Hertwig's full account of his observations, with figures, in the 4th vol. of the Morphologische Jahrbuch, has appeared since the above was written. The figures given strongly support Hertwig's views.
[365] Flemming (6) finds that, in the summer and probably parthenogenetic eggs of Lacinularia socialis, the germinal vesicle approaches the surface and becomes invisible, and that subsequently a slight indentation in the outline of the egg marks the point of its disappearance. In the hollow of the indentation Flemming believes a polar cell to be situated, though he has not definitely seen one.
[366] The instances quoted by Siebold from Hensen and Oellacher are not quite satisfactory. In Hensen's case impregnation would have been possible if we can suppose the spermatozoa to be capable of passing into the body-cavity through the open end of the uninjured oviduct; and though Oellacher's instances are more valuable, yet sufficient care seems hardly to have been taken, especially when it is not certain for what length of time spermatozoa may be able to live in the oviduct. For Oellacher's precautions, vide Zeit. für wiss. Zool. Bd. XXII. p. 202.
[367] According to Hertwig's most recent statement a nucleolus is present in this nucleus.
[368] The recent researches of Calberla on the impregnation of the ovum of Petromyzon Planeri support this conclusion.
[369] This seems the most probable view with reference to the nature of the head of the spermatozoon, though the point is not perhaps yet definitely decided.
XII. On the Structure and Development of the Vertebrate Ovary[370].
(With Plates 24, 25, 26.)