Mr. Spencer thinks that the non-transmission of acquired modifications is incongruous with the great fact of atavism. But the great law of the inheritance of that which is a development of the transmissible type does not necessarily imply the inheritance of modifications acquired by the individual. Because English children may inherit blue eyes and flaxen hair from their Anglo-Saxon ancestors, it by no means follows that an Englishman must inherit his father's sunburnt complexion or smooth-shaven face. Of course atavism ultimately adopts many instances of revolt against its sway. But to assume that these changes of type _follow_ the personal change rather than cause it, is to assume the whole question at issue. That like begets like is true as a broad principle, but it has many exceptions, and the non-heredity of acquired characters may be one of them. FOOTNOTES: [2] _Principles of Biology_, Sec. 166, footnote. The English jaws are somewhat lighter than the Australian jaws, though I could not undertake to affirm that they are really shorter and smaller. In the typical skulls depicted on p. 68 of the official guide to the mammalian galleries at South Kensington, the typical Caucasian jaw is very much larger than the Tasmanian jaw, although the repulsively obtrusive teeth of the latter convey the contrary idea to the imagination. Mr. Spencer's assumption that the ancient Britons had large jaws appears to me erroneous. (See Professor Rolleston's _Scientific Papers and Addresses_, i. p. 250.) [3] Romanes, Galton, and Weismann have made great use of this principle in explaining the diminution of disused organs. Weismann has given it the name of _Panmixia_,--_all_ individuals being equally free to survive and commingle their variations, and not merely selected or favoured individuals. See his _Essays on Heredity_, &c., p. 90 (Clarendon Press). [4] Inclusive in each case of fixed strengthening wire weighing about a sixteenth of an ounce or less. [5] References of course are to _Factors of Organic Evolution_. [6] P. 13; and _Nineteenth Century_, February, 1888, p. 211.