INDIVIDUAL DIFFERENTIATION AND ADAPTATION. 121 



most numerous illustrations of this are found. The walking- 

 stick insect appears as dead twigs when not in motion. Many 

 butterflies resemble leaves, when at rest. A noted instance is 

 Kallima which is a large species, conspicuous when flying be- 



FIG. 59- 



FIG. 59. Walking-stick insect (Diapheromera veliei) on twig. Natural size. By 



J. W. Folsom. 



Questions on the figure. To what group of insects does this belong? 

 Do you see any reason to suppose that it illustrates protective resemblance? 



cause of blue and orange patches on the upper surface of the 

 wings. The wings are folded when at rest and the lower sides 

 are colored and marked so like a dead leaf that the deception 

 is very complete. The larvae of some of the geometrid moths, 

 often called " measuring-worms," are remarkably like the 

 twigs on which they crawl, both in color and shape. This is 

 made more striking by the presence of roughnesses on the sur- 

 face which suggest buds, and by the possession of muscles 

 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 ccelenterates, bees, some spiders, a few 



