130 ZOOLOGY 



which enable them to support themselves rigidly outstretched 

 for hours by means of the posterior legs alone, so that the 

 axis of the body makes an angle with the branch. 



Other instances of special devices whereby animals protect 

 themselves are found in the electric organs of some eels and 

 other fishes, in the poisonous fluids with or without special 

 stinging organs, as in coelenterates, bees, some spiders, a few 

 fishes (spines), and some snakes; also in the repulsive odors of the 

 skunk and many caterpillars. 



Caterpillars oftentimes have an acrid or otherwise unpleasant 

 taste, but, unless this is associated with a special odor or color 

 by which its enemies may recognize the fact, it is not likely to 

 prove of any great service to the animal possessing it since a sin- 

 gle incision in the soft body made by the bill of a bird is likely to 

 cause death. For similar reasons animals with stings are often 

 highly colored. The colors or other marks are, in these cases, in 

 the nature of warnings. The "monarch," one of our large con- 

 spicuous butterflies is an illustration of the association of color 

 and offensive taste; the wasps and the coral-snake, of the asso- 

 ciation of color with the possession of stinging powers. Thus 

 owing to the power of association in the mind of the enemies, 

 the advantage comes to lie quite as much in the possession of 

 the special color or form as in the presence of the underlying 

 protective powers. These facts give rise to the remarkable phe- 

 nomena called mimicry. This term applies to those instances 

 where an edible or harmless animal, by reason of its similarity 

 to those which are disagreeable, partakes of their immunity 

 from attack. Mimicry must not be considered as in any way 

 a matter of choice with the animal but simply the result of 

 natural selection in preserving and allowing the propagation 

 of favorable variations. The viceroy butterfly, though edible, 

 seems to be protected by its striking likeness to the monarch. 

 The nearest relatives of the viceroy are quite differently marked. 

 Mimicry of bees and wasps is found among many flies and some 

 moths and beetles. Non- venomous snakes occasionally have 

 the marking and the motions of the venomous. 



164. Practical Exercise. — Try to discover instances of general protective re- 

 semblance among the animals known to you. Analyze each case and see just 



