72 CALIFORNIA ACADEMY OF SCIENCES. 



of the organism, which last is determined by nutrition. 

 The law of sexual intensification would thus seem to be 

 applicable to any form of modification, which may be 

 encouraged by natural selection, in which the male takes 

 the lead, but would in no wise serve to originate any new 

 part or structure. 



At first sight this law might appear to be a mere re- 

 statement of the view of Dr. W. K. Brooks. According 

 to his view, the male cells are the bearers of gemmules 

 inducing variation, and in hard times the variable males 

 being in preponderance, would induce progressive varia- 

 tion. Rev. J. T. Gulick has criticised this view as fol- 

 lows:* " There can be no doubt that in many species 

 the males are more variable than the females, and that 

 in some of the same species the proportion of males in- 

 creases with the degree of adversity; but this does not 

 seem to be sufficient ground for maintaining that the 

 increase in the proportion of males will increase the 

 variability of the offspring. Increase in the number or 

 amount of the variable element does not necessarily in- 

 volve increase in the variability of either element, or in 

 the offspring of both. I find need of additional factors 

 in order to bring these facts into any relation to the in- 

 crease of variability. Granting that the sperm-cell is 

 the source of variation and the germ-cell the source of 

 fixity, and that increased tendency to variation in the 

 offspring will be secured by an increased range of varia- 

 tion in the sperm-cells, it does not follow that increase 

 in the relative number of males will increase the range 

 of variation in the sperm-cells, and therefore in the off- 

 spring." 



This difficulty, which implies that, however great the 

 majority of the variable sex may be, unless each one 



* Journ. Linu. Soc., xxiii, p. 317. 



