rROTECTIVE COLOEATTON. 9'3' 



iguana, resting motionless upon the brancli of a tree, seems to 

 be a perfect case of protective coloration. We learn, however, 

 that a species in the island of Sta. Lucia is easily captured in 

 spite of its colour ; the iguana in question is highly esteemed 

 as an article of food, and is hunted by means of dogs; it is not 

 pretended that the dogs can see their quarry, but they detec^t 

 its presence by the sense of smell. The iguanas of Soutli 

 America, some of which have the same coloration, may fall 

 an easy prey to jaguars and ocelots guided by the same sense. 

 It is true that the cat tribe do not appear to have quite so 

 keen a nose as dogs; but they belong to those Mammalia which 

 have been termed, on account of the large development of that 

 part of the brain which is concerned with smelling, " osmatic " 

 as distinguished from the Primates and aquatic mammals, 

 which have at most a very slightly marked " rhinencephalon." 



Protective Coloration occasionally appears to be Superfluous. 



It is not, of course, fatal to the theory that various colour 

 modifications have gradually arisen through elimination, to be 

 able to show that disguises are sometimes seen through, and 

 warning colours occasionally disregarded. Any quality which 

 gives to its possessor the smallest advantage in the struggle. 

 for existence may be seized upon and perpetuated by natural 

 selection. At the same time we must carefully avoid assuming 

 that a given disguise is effective, without abundant experi- 

 mental proof. Nor does it necessarily follow that a gaudily 

 coloured caterpillar rejected with signs of disgust by one 

 lizard will be refused by another. Animals have their likes 

 and dislikes, just as we have. Experimental evidence that 

 this is so is given on pages 164, 16.3. All these matters must 

 be carefully considered before framing hypotheses ; the diffi- 

 culties arising chiefly from our imperfect knowledge, and 



