3 12 Habit and Instinct. 



less complexity will be eliminated, the little more com- 

 plexity will survive. The little less and the little more are, 

 however, in the same line of developmental swing. Hence, 

 the variations discoverable in fossil mammals in which 

 tooth-development along special lines is in progress, will, 

 on the hypothesis of selection, be plus and minus along a 

 given line; in other words, the variations will be deter- 

 minate, and in the direction of special adaptation." 



Prof. Weismann adopts a similar position in his recent 

 paper on Germinal Selection. He says,* "By the selection 

 alone of the plus or minus variations of a character is the 

 constant modification of that character in the plus or 

 minus direction determined. . . . We may assert therefore, 

 in general terms, that a definitely directed progressive 

 variation of a given part is produced by continued selec- 

 tion in that definite direction. This is no hypothesis, 

 but a direct inference from the facts, and may also be 

 expressed as follows : By selection of the kind referred 

 to, the germ is progressively modified in a manner cor- 

 responding with the production of a definitely directed 

 progressive variation of the part." 



In his Komanes Lecture, Prof. Weismann makes another 

 suggestion which is valuable and may be further deve- 

 loped. He is there dealing with what he terms " intra- 

 selection " f — or that which gives to the individual it& 

 plasticity. One of the examples that he adduces is the 

 structure of bone. " Hermann Meyer," he says, % " seems 

 to have been the first to call attention to the adaptiveness 

 as regards minute structure in animal tissues, which is 



* Monist, January, 1896, p. 2C8. 



t Prof. Mark Baldwin's " organic selection " appears to be a new and not 

 very satisfactory term for the same process. 



% Eomanes Lecture on " The Effect of External Influences on Develop- 

 ment" (1894), pp. 11, 12. 



