356 



ELEMENTARY BIOLOGY 



the animal. But this involves some way of educating the 

 enemies as to the meaning of the warning. It is true that 

 many animals instinctively avoid certain kinds of plants and cer- 

 tain kinds of animals, and that some of the avoided species are 



really injurious. It is also true 

 that animals are. often poisoned 

 by eating unsuitable organisms, 

 and that animals often eat organ- 

 isms that are distasteful or that 

 make them sick. 



A young chick, fresh from the 

 egg, soon begins pecking about 

 for food. A chick finds a worm 

 or a caterpillar and at once eats 

 it. Most of the material thus 

 taken is sufficiently palatable. But 

 presently the chick finds a hornet 

 or a woolly-bear caterpillar. This 

 mouthful is somewhat too much 

 for the chick ; it makes a profound 

 impression on the young animal. 

 The hornet may be killed, or the 

 caterpillar may be killed, but the 

 chick is impressed. She will never 

 eat that kind of food again. The 

 dead hornet or caterpillar has 

 taught the chick a lesson, but can- 

 not get the benefit of the lesson. 

 Other hornets, however, or other 

 woolly bears, are safe, so far as 

 that particular chicken is concerned. 



The individual sample is thus sacrificed for the benefit of the species. 

 When we consider that every individual has to have his own lesson, 

 we should think this a rather expensive mode of protection, but we 

 may take the idea for what it is worth. One thing is certain, many 

 conspicuous species lack the bitter juice, while others have the bitter 

 juice, and yet lack a conspicuous appearance ; and one species seems 

 to hold its own about as well as another. 



FIG. 173. Mimicry among butterflies 



The viceroy, , belongs to a different 

 genus of butterflies from the monarch, 

 or milkweed butterfly, a ; yet the sesem- 

 blance at first glance is so striking that 

 most people will be unable to point out 

 any difference between the two except in 

 size. A close study will show us, however, 

 a number of differences in the pattern 



