[45] Scientific Papers and Addresses, II, pp. 862-3. [46] English trans., 2nd edition (1903), p. 159. [47] The Cell, p. 434. [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. [51] The actual stimulus which prompts the division is probably to be found in the disturbance of equilibrium which arises when the cell is taking in more nutriment than its digestive system can deal with. This, of course, does not explain why it should divide instead of dying of indigestion. [52] See Strasburger, _loc. cit._ [53] The Evolution Theory, I, 402-3. [54] The subject of degenerated and lost organs is very fully treated by M. Edmond Perrier in his Traité de Zoologie, pp. 325 _sqq._ It may be noted that animals which are _fixed_ usually lack eyes, even in light. In the depths of the sea, where total darkness reigns except for the phosphorescence emitted by certain animals, it is found that some creatures have completely lost their organs of sight, while others have them extraordinarily developed. Those which have lost them are the walkers (_Crustaceæ_); those which show an exceptional development are the swimmers. This goes to show that the needs of the animal, rather than the external conditions, are the determining cause.