68 CALIFORNIA ACADEMY OF SCIENCES. 



in a passive growing state and storing away energy, it 

 is spoken of as anabolic, but when it is in a disruptive 

 condition, giving out energy and breaking up into 

 simpler compounds it is said to be katabolic. The 

 metabolism of an organism is constantly varying be- 

 tween the anabolic and katabolic state, although of course 

 not in rhythms of definite duration. 



Messrs. Geddes and Thomson have devoted a consider- 

 able space in their work on the Evolution of Sex to estab- 

 lishing the principle that the male nature is naturally 

 katabolic, the female naturally anabolic. They have en- 

 forced this principle by many examples and arguments, 

 and it is justifiable, it seems to me, to use it as a work- 

 ing hypothesis. The law of sexual intensification pro- 

 posed by me in a recent paper on the Colors of West 

 Coast Mammals* is based upon this principle. Among 

 west coast mammals are certain species which have as- 

 sumed a black color in harmony with their Surround- 

 ings, which are dark in hue, owing to the volcanic rock 

 of which the soil is formed. A particular species was 

 taken as an example, the black-headed ground squirrel 

 {Sj^eriiiophilus grammurus atricapilhts) , and an attempt 

 was made to account for the black color. For three 

 reasons it was assumed that the ancestors of this species 

 were paler in color, probably gray or brown: (1) Be- 

 cause black is never a primitive color but rather a mark 

 of specialization. (2) Because the races and species 

 which are not black occupy a much greater geographical 

 area, the black form being very local; and (3), be- 

 cause the young are 'paler than the adult. If the pre- 

 ceding discussion has established the impossibility, or 

 even the improbability of natural selection exercising a 

 creative power, it becomes proper to ask how the black 



*Zoe, ii, pp. 203-216. 



