VIEWS OF ERASMUS DARWIN 221 



the means of escaping other animals more powerful 

 than themselves.* Hence some animals have acquired 

 wings instead of legs, as the smaller birds, for pur- 

 poses of escape. Others, great length of fin or of 

 membrane, as the flying-fish and the bat. Others 

 have acquired hard or armed shells, as the tortoise 

 and the Echinus marinus (p. 239). 



" The colors of insects," he says, " and many smaller 

 animals contribute to conceal them from the dangers 

 which prey upon them. Caterpillars which feed on 

 leaves are generally green ; earthworms the color of 

 the earth which they inhabit ; butterflies, which fre- 

 quent flowers, are colored like them ; small birds 

 which frequent hedges have greenish backs like the 

 leaves, and light-colored bellies like the sky, and are 

 hence less visible to the hawk, who passes under them 

 or over them. Those birds which are much amongst 

 flowers, as the goldfinch {Fringilla carduelis), are fur- 

 nished with vivid colors. The lark, partridge, hare, 

 are the color of dry vegetables or earth on which 

 they rest. And frogs vary their color with the mud 

 of the streams which they frequent ; and those which 

 live on trees are green. Fish, which are generally 

 suspended in water, and swallows, which are generally 

 suspended in air, have their backs the color of the 

 distant ground, and their bellies of the sky. In the 

 colder climates many of these become white during 

 the existence of the snows. Hence there is apparent 

 design in the colors of animals, whilst those of vege- 



* The subject of protective mimicry is more explicitly stated by 

 Dr. Darwin in his earlier book, The loves of the Plants, and, as 

 Krause states, though Rflsel von Rosenhof in his Insekten-Belusti- 

 gungeti (Nurnberg, 1746) describes the resemblance which geo- 

 metric caterpillars, and also certain moths when in repose, present to 

 dry twigs, and thus conceal themselves, , ' this group of phenomena 

 seems to have been first regarded from a more general point of view 

 by Dr. Darwin." 



