SOCIAL LIFE OF ANIMALS 489 



Mimicry. (Protective Resemblance.) — Some butterflies resem- 

 ble a leaf, certain beetles mimic the wasp, certain harmless flies 

 mimic bees and are preserved from destruction by birds. The 

 walking stick insect resembles twigs. Some harmless snakes resem- 

 ble in markings venomous forms such as the coral snake. (See 

 Fig. 176.) 



References on Animal Coloration 



Beddard, F. E. 1892. Animal Coloration. 



Poulton, E. B. 1890. Colors of Animals. 



Roosevelt, T. African Game Trails. 



Thayer, A. H. 1909. Concealing Coloration in the Animal Kingdom. 



Geographical Distribution 



A similar environment does not always explain the appearance 

 of like forms. If we are to accept the theory that all forms are 

 derived from a common ancestor, we can readily explain some of the 

 following facts: 



(a) The llamas of South America have as their nearest living 

 relatives the camels living in the deserts of Asia. In Oregon one 

 finds fossil llamas. {^) The Australian kangaroo has no relatives 

 nearer than the opossum. Neither is found in its native home, which 

 was Europe. How did they reach South America and Australia? 

 (c) The plants of Madagascar are not related to those of Europe 

 while both plants and animals of North America and Eastern Asia 

 are similar. Why? 



Explanation. — Present barriers have not always existed, and 

 land connections that once joined continents have disappeared, 

 separating closely related forms. Climatic changes have also 

 produced cataclysmic effects. 



Dispersal of Small Forms. — In the case of smaller forms, we 

 find that dispersal is effected quite readily. Protozoa and the eggs 

 and larvae of numerous worms and Rotifers are transported by 

 birds and other animals, as well as attached to wind-blown or 

 floating debris. It is well known that the glochidia of fresh water 

 mussels are carried long distances attached to the gills and fins of 

 fishes. 



Again, driftwood bears strange companions to far distant islands. 

 Beebe on his Arcturus voyage counted on one floating log 54 species 

 of marine crabs, worms and fishes. 



