Weismann's Explanation of Coordinated Variations 215 



every fortuitous variation that is possible, both plus and 

 minus, actually develops, the net result after the elimi- 

 nation of the minus variations must be that the muscles 

 would be stronger. But this initial increase, this first 

 impulse toward strengthening, would be in turn the 

 cause of a phylogenetic tendency to a further strengthen- 

 ing, because it would indicate that these muscles were 

 represented in the germ plasm by determinants which 

 are endowed with a greater power of growth, and con- 

 sequently with greater power of assimilation. "The 

 affluence of nutritive fluids would become proportionally 

 augmented and would contribute likewise to giving the 

 plus variations a preponderance over minus variations. 

 There would thus be a phylogenetic tendency toward the 

 continual increase of these muscles and it would endure 

 just as long as the increase in the weight of the head, 

 and would stop when the latter stopped. For in this 

 case the plus variations of the determinants would be 

 eliminated by individual selection, as soon as they 

 attained selectable value." 163 



But this artificially constructed hypothesis, which did 

 not hold good at all in the case of rudimentary organs, 

 is still less adapted to the case of co-ordinated varia- 

 tions. For in these phenomena it appears still more 

 clearly that in phylogenetic changes there are concerned 

 not simply exclusively plus or minus variations, but 

 transformations which might be constituted by a com- 

 bination of increases in one direction and decreases in 

 another, or might not be susceptible of being decomposed 

 into merely quantitative variations. It should be noted 

 further that for certain correlative, histological varia- 



163 Weismann : Neue Gedanken zur Vererbungsfrage. P. 22. 



