[8] Stephane Leduc, in his _Théorie Physico-chémique de la vie_ (Paris, 1910), endeavors to trace all the above phenomena to the simple action of diffusion and osmose (see ch. viii, on _Karyokinesis_) but though the resemblance of some of the forms above described to diffusion-figures is interesting—as also is their resemblance to the forms of magnetic fields—this does not prove their genesis either from diffusion or magnetism. It only makes probable that some of the phenomena in question are related to the very obscure forces of diffusion or magnetism—a thing which, of course, is already admitted and recognized. With regard to all this the reader should study the astonishing resurrection of the mature blow-fly from the mere milky pap which is all that the pupa at a certain stage consists of. (See _The Biology of the Seasons_, by J. Arthur Thomson, 1911.) [9] “In every known case an essential phenomenon of fertilization is the union of a sperm nucleus of paternal origin with an egg nucleus of maternal origin, to form the primary nucleus of the embryo. This nucleus ... gives rise by division to all the nuclei of the body, and hence every nucleus of the child may contain nuclear substance derived from both parents” (_The Cell in Development and Inheritance_, by E. B. Wilson, Macmillan Co., 1904, p. 182). [10] The latter, of course, being just discernible by the naked eye. [11] _Parallel Paths_, by T. W. Rolleston (Duckworth, 1908), p. 53. [12] _Parallel Paths_, p. 52. See also, for further accounts, _The Evolution of Sex_, pp. 112–14; _The Plant Cell_, by H. A. Haig, pp. 121, 123 _et seq._; Die Vererbung, by Dr. E. Teichmann (Stuttgart, 1908), pp. 39, 40, &c. Throughout it must be remembered that these ‘maturation’ processes in the generative cells are not only exceedingly complex, but also very various in the various plants and animals; and the reader should be warned against too easily accepting ready-made descriptions and generalizations supposed to fit all cases. [13] Here and elsewhere in his book Professor Wilson uses “germ-cells” to include “sperm-cells”; and I have indicated this by the bracket. [14] _The Cell_, p. 285. [15] It appears that in the ordinary conjugation of Protozoa a quite similar process is observable. [16] “Nowhere in the history of the cell do we find so unmistakable and striking an adaptation of means to ends or one of so marked a prophetic character, since maturation looks not to the present but to the future of the germ [and sperm] cells” (_The Cell_, p. 233).