360 EVOLUTION, GENETICS, AND GENETICS 



and making the environment visible. Could man view the sea bottom 

 through some of these instruments, he would doubtless add something 

 very novel and weird to his scenic repertoire. 



Other creatures of the darkness live strange lives in caves, such as 

 ihe Mammoth Cave of Kentucky. Most cave dwellers are blind or 

 nearly so, and usually have a pale and ghostlike appearance because of 

 their lack of pigment. All grades of defective eyes are found, ranging 

 from those that are merely somewhat smaller than normal to those 

 that remain deeply imbedded in the head in a relatively undifferen- 

 tiated state. It goes without saying that such animals are better 

 adapted to life in caves than they would be outside. One pressing 

 problem of biology is : How did the cave animals become blind? Did 

 they wander into the caves as normal animals and become blind be- 

 cause their eyes were disused, or did they become blind outside through 

 no fault of their own, as the result of a mutation, and by chance find 

 safety in an underground stream or a cave? The first explanation is 

 Lamarckian, the second Darwinian. 



COLOR AND PATTERN IN ANIMALS 



"The phenomena of color in both animals and plants," says 

 Metcalf, 1 "are among the most remarkable and interesting in the 

 whole realm of nature. It is not so much the way in which the color 

 is produced, whether by pigments or by refraction, that interests us 

 in this connection, as it is the uses to which colors are put. Let us 

 first refer to the colors of animals. 



"According to the uses to which colors in animals are put, we 

 may classify them, for purposes of description, as follows: 



"IndiiTerent coloration, not useful, so far as we can judge; 



Colors of direct physiological value; 



Protective coloration and resemblances; 



Aggressive coloration and resemblances; 



Alluring coloration and resemblances; 



Warning coloration; 



Immunity coloration; 



Mimetic coloration and resemblances; 



A. Protective 



B. Aggressive 



Signals and recognition marks; 



Confusing coloration; 



Sexual coloration." 



' M. M. Metcalf, Organic Evolution (191 1). 



