DEVELOPMENT 429 



certain butterflies on the Amazon have such a strong 

 odor that the birds let them alone ; and butterflies of an- 

 other family in the same region have assumed for pro- 

 tection the same form and color of wing, but lack the 

 odor. So we have beelike moths, beetlelike crickets, 

 wasplike flies, and antlike spiders ; harmless and venom- 

 ous snakes copying each other, and orioles departing 

 from their usual gay coloring to imitate the plumage, 

 flight, and voice of quite another kind of birds. The 

 species which are imitated are much more abundant than 

 those which mimic them. There is also a general har- 

 mony between the colors of an animal and those of its 

 habitation {protective resemblance). We have the white 

 polar bear, the sand-colored camel, and the dusky twilight 

 moths. There are birds and reptiles so tinted and mottled 

 as exactly to match the rock, or ground, or bark of a 

 tree they frequent ; and there are insects rightly named 

 "walking sticks" and "walking leaves." These coin- 

 cidences are often beneficial to the imitating species. 

 Generally, they wear the livery of those they live on, 

 or resemble the forms more favored than themselves. 



Again, some animals which have a nauseous taste or 

 odor, as certain caterpillars, insects, salamanders, etc., 

 advertise the fact by being brilliantly colored and spotted 

 (warning coloration), and are thus protected against other 

 animals which would prey upon them. 



5. Homo logy, Analogy, and Correlation 



The tendency to repetition in the development of 

 animals leads to some remarkable affinities. Parts or 

 organs, having a like origin and development, and 

 therefore the same essential structure, whatever their 

 form or function, are said to be homologous ; while parts 

 or organs corresponding in use are called analogous. 



