[35] Prof. Wilson’s work on the cell (see note on p. 33) may be referred to for a comprehensive and detailed statement of all that is known at present on this subject.
[36] According to Wilson (_op. cit._) this was guessed by Haeckel in 1866, and confirmed in 1884-5 by the almost simultaneous discoveries of O. Hertwig, Strasburger, Kölliker, and Weismann.
[37] Sixteen have been counted in the human cell. A grasshopper has twelve, a lily twenty-four. The number is almost always an even one, but as with everything in Nature there are exceptions to the rule.
[38] The process briefly described above is that of ‘mitotic’ division (μίτος, a thread, from the appearance of the chromosomes). Amitotic division, in which the cell and nucleus simply divide in two without the formation of chromosomes, also occurs under certain conditions, but is usually an abnormal or degenerative process (cf. Wilson, The Cell, pp. 116-119).
[39] “Every animal appears as a sum of vital entities, each of which bears within itself the complete character of life” (Virchow, Cellular-pathologie, p. 12, 1858).
[40] Weismann, The Evolution Theory, I, 251.
[41] It is cast out into the cytoplasm—the substance surrounding the nucleus—where it degenerates (see Wilson, The Cell, p. 147).
[45] Scientific Papers and Addresses, II, pp. 862-3.
[46] English trans., 2nd edition (1903), p. 159.
[48] Against this view might be quoted the fact that the unfertilized eggs sometimes laid by the workers (imperfect females) of bee and ant communities always develop into drones.
[49] Pp. 262-3. The bird was examined by Prof. Max Weber, of Amsterdam, and Mr. Beddard refers to the _Zoologischer Anzeiger_ for 1890, p. 508, for Weber’s account of the case.
[50] The now famous Mendelian Law of Inheritance, first discovered in 1865 by Mendel, an Augustinian monk and Abbott of Brünn, and completely ignored till the year 1900, when it was rediscovered by De Vries and others, is also strongly confirmatory of Weismann’s analysis of the principle of heredity. According to this law it is possible, as it were, to isolate any particular characteristic of a species or even (if heritable) of an individual, and by a definite system of crossing to attach this characteristic _alone_ to any other variety capable of crossing with the first. This means that inheritance is governed by separable units of formative energy. These units are Weismann’s determinants. The discovery of the methods of turning this principle to practical account is obviously of great importance for agriculture and stockbreeding. The law has some inexplicable limitations which are now closely engaging the attention of biologists. It is impossible to enter upon the subject more fully here, but a good account of it will be found in Lock’s Recent Progress in the Study of Variation, and in a brochure, An Address on Mendelian Heredity, by W. Bateson, reprinted from _Brain_, pt. cxiv, 1906.