[88] Organologische Studien, Zweites Heft.
[89] “Beiträge z. Entwicklungsgeschichte der Knochenfischen.” Zeit. für Wiss. Zoologie. Bd. XXII. 1872.
[90] The memoirs of Auerbach and Strasburger (Zellbildung u. Zelltheilung) have unfortunately come into my hands too late for me to take advantage of them. Especially in the magnificent monograph of Strasburger I find drawings precisely resembling those from my specimens already in the hands of the engraver. Strasburger comes to the conclusion from his investigations that the modified nucleus always divides and never vanishes as is usually stated. If his views on this point are correct part of the hypothesis I have suggested above is rendered unnecessary. The striæ of the protoplasm, which in accordance with Auerbach's view I have considered as being due to a streaming out of the matter of the nucleus, he regards as resulting from a polarity of the particles in the cell and the attraction of the nucleus. My own investigations though, as far as they go, quite in accordance with those of Strasburger, do not supply any grounds for deciding on the meaning of these striæ; and in some respects they support Strasburger's views against those of other observers, since they demonstrate that in Elasmobranchii the modified nucleus does actually divide.
[91] This is the view which has been taken by Auerbach (Organologische Studien).
[92] Loc. cit.
[93] After Strasburger's observation it must be considered very doubtful whether the streaming out of the contents of the nucleus, in the manner implied in the text, really takes place.
[94] Entwicklungsgeschite der Unke, Pl. 1, fig. 18.
[95] As I before mentioned, Strasburger (Zellbildung u. Zelltheilung) has represented bodies precisely similar to those I have described, which appear during the segmentation in the egg of Phallusia mammillata as well as similar figures observed by Butschli in eggs of Cucullanus elegans and Blatta Germanica. The figures in this monograph are the only ones I have seen, which are identical with my own.
[96] Morphologisches Jahrbuch, Bd. 1. pp. 46, 47.
[97] Strasburger's (loc. cit.) arguments about the influence of the nucleus in cell division are not to my mind conclusive; though not without importance. It is difficult to reconcile his views with the facts of cell division observable during the Elasmobranch segmentation; but even if their truth be admitted they do not bring us much nearer to a satisfactory understanding of cell division, unless accompanied (and at present they are not so) by a rational explanation of the forces which produce the division of the nucleus.