PFLuGER: _Die teleologische Mechanik der lebendigen Natur_; Bonn, 1877.
MAUPAS: _Sur le determinisme de la sexualite chez l'Hydatina senta._ _Comptes rendus des seances de l'Academie des Sciences_; Paris, 1891.
WEISMANN: _Die Allmacht der Naturzuchtung. Eine Erwiderung an Herbert Spencer_; Jena, 1893.
HERBERT SPENCER: _A Rejoinder to Professor Weismann._ _Contemporary Review_, 1893.
Ibid.: _Die Unzulanglichkeit der 'Naturlichen Zuchtwahl.'_ _Biol.
Centralblatt_, vol. xiv., No. 6.
EMERY: _Die Entstehung und Ausbildung des Arbeiterstandes bei den Ameisen._ _Biol. Centralb._, vol. xiv., No. 2, 1894.
HAACKE; _Gestaltung and Vererbung_ (1894).
[18] The assumption of doubling division does not involve the assumption that the germinal mass is unalterable. Although I do not regard the process of division as a mechanism for breaking up the idioplasm into dissimilar groups of determinants, I regard the idioplasm--and here I agree with Naegeli--as only relatively stable. In course of time external and internal forces may slowly alter it. On the one hand, the idioplasm of the reproductive cells in the course of generations may slowly alter, while, on the other hand, the idioplasm of cell groups in an organism may acquire a local character in correspondence with their different topographical and functional positions in the whole creature, and in relation to their place in the organic division of labour, just as in human communities individuals become altered by the lifelong exercise of some calling.
Nor does the doctrine of doubling divisions conflict with those conclusions of pathology according to which, in the process of regeneration, cells and tissues give rise only to cells and tissues of their own order. For further details see my treatise, _Ei und Samen-Bildung bei Nematoden_, pp. 97-99.
These slight suggestions are only to prevent misconceptions.