386 BIOLOGY AND ITS MAKERS 



reduced in their development, rather than increased; but 

 manifestly the short-winged race of beetles is better adapted 

 to live under the particular conditions that surround their 

 life in these islands. 



While this is not a case of increase in the particular organ, 

 it illustrates a progressive series of steps whereby the organ- 

 ism becomes better adapted to its surroundings. A similar 

 instance is found in the suppression of certain sets of organs 

 in internal parasites. For illustration, the tapeworm loses 

 particular organs of digestion for which it does not have 

 continued use ; but the reproductive organs, upon which the 

 continuance of its life depends, are greatly increased. Such 

 cases as the formation of short-winged beetles show us that 

 the action of natural selection is not always to preserve what 

 we should call the best, but simply to preserve the fittest. 

 Development, therefore, under the guidance of natural selec- 

 tion is not always progressive. Selection by nature does 

 not mean the formation and preservation of the ideally per- 

 fect, but merely the survival of those best fitted to their 

 environment. 



Color.- -The various ways in which natural selection acts 

 are exceedingly diversified. The colors of animals may be 

 a factor in their preservation, as the stripes on the zebra 

 tending to make it inconspicuous in its surroundings. The 

 stripes upon the sides of tigers simulate the shadows cast by 

 the jungle grass in which the animals live, and serves to con- 

 ceal them from their prey as well as from enemies. Those 

 animals that assume a white color in winter become thereby 

 less conspicuous, and they are protected by their coloration. 



As further illustrating color as a factor in the preserva- 

 tion of animals, w r e may cite a story originally told by 

 Professor E. S. Morse. When he was collecting shells on the 

 white sand of the Japanese coast, he noticed numerous white 

 tiger-beetles, which could scarcely be seen against the white 



