THE METHOD OF CEEATION OF ORGANIC FORMS. 211 



intelligence, and the adoption of means for obtaining it still 

 greater ones. It is here that intelligent selection proves its su- 

 premacy as a guide of use, and consequently of structure, to all 

 the other agencies here proposed. The preference for vegetable 

 or for animal food determined by the choice of individual animals 

 among the omnivores, which were, no doubt, according to the 

 paleontological record, the predecessors of our herbivores, and per- 

 haps of carnivores also, must have determined their course of life 

 and thus all their parts, into these totally distinct directions. 

 The choice of food under ground, on the ground, or in the trees , 

 would necessarily direct the uses of organs in the appropriate 

 directions respectively. 



In the selection of means of defense a minor range of choice is 

 presented. The choice must be limited to the highest capabilities 

 of the animal, since in defense, these will, as a general thing, be 

 put forth. This will, however, not be necessarily the case, but 

 will depend in some measure on the intelligence of the animal, as 

 we readily observe in the case of domesticated species. 



In the case of the rattlesnake, already cited, the habit of rapid 

 vibration of the tail appears to me to be the result of choice, and 

 not of compulsion. For the cobra of India, for the same pur- 

 pose, expands the anterior ribs, forming a hood, which is a very 

 different habit.* Here are two alternatives, from which choice 

 might be made, and violent hissing is a third, which the species 

 of the colubrine genus PityopMs have adopted to some purpose. 

 As to the benefit of the rattle, it no doubt protects the animal 

 from all foes other than man ; but is rather a disadvantage as re- 

 gards the latter, being by a beautiful turn of events a protection 

 to the higher animal. 



On the principle of natural selection it might be supposed that 

 the harmless snakes which imitate the Cro talus for the sake of 

 defense were preserved ; but if the above explanation of the origin 

 of the habit in the latter be true, the second explanation is not 

 valid. (Since in time the harmless snakes preceded the rattle- 

 snakes. Ed. 188G,) 



The power of metachrosis, or of changing the color at will, by 

 the expansion imder nerve-influence of special pigment cells, exists 

 in most Reptilia, Batrachia, and fishes. It is then easy to believe 

 that free choice should, under certain circumstances, so habitually 



* The North American Heterodons possess a similar habit. (Ed. 1886.) 



