Of course there must also be unimportant changes in butterfly-markings which depend solely on the internal play of forces in the determinant system, and to this must be referred the markings of many of the 'variable' species whose variations are mere fluctuations in the details of marking, which have therefore caused much trouble to the systematists. Truly unimportant variations will rarely or never combine into a 'constant' form, and the fact that there are species which are 'variable' in such a high degree is enough to make us refer their variations to their lack of importance, for if they possessed any biological value the less valuable among them would gradually be removed by selection. Perhaps the variable species of certain moths like _Arctia caja_, and especially _Arctia plantaginis_, the little 'bear' of the Alps and Apennines, must be reckoned among these. But from the fact that there are such fluctuations in the markings of Lepidoptera, it seems to me that we must conclude that species which show a high degree of constancy in their markings have been influenced by selection, or by climatic influences which turned the play of forces within the determinant system in the same direction in all individuals. All these considerations and conclusions are quite sound and serviceable theoretically, but they are difficult to apply to individual cases, and where this is attempted it must be with the greatest caution, and, if possible, on a basis of investigations specially undertaken for the purpose; for how should we know whether a species which to-day is highly variable may not a geological epoch later become a very constant one? We must in any case assume that marked fluctuations of characters are associated with many transformations. LECTURE XXVI GERMINAL SELECTION (_continued_) Germinal selection, spontaneous and induced--Climatic forms of _Polyommatus phlæas_--Deformities--Excessive augmentation of variations--Can it lead to the elimination of a species?--Saltatory variations, copper-beech, weeping trees--Origin of sexual distinguishing characters--Formation of breeds among domesticated animals--Degenerate jaws--Human teeth--Short-sightedness--Milk-glands--Small hands and feet--Ascending variation--Talents, intellect--Combination of mental endowments--The ultimate roots of heritable variation--There are only plus- and minus-variations--Relations of the determinants to their determinates--The play of forces in the determinant system of the id--Germinal selection inhibited by personal selection--Objection on the score of the minuteness of the substance of the germ-plasm.