334 GENERAL ZOOLOGY 



A. jeffersonianum which lacks the spots. If one adopts the view 

 that in the case of Hyla the green color is protective, one must 

 also admit that in other cases the coloration is of no particular 

 protective significance. That does not necessarily destroy the 

 value of protective coloration to some animals. 



Arctic mammals such as the polar bear, Thalarctos maritimus, 

 and some other arctic mammals, are white in conformity with the 

 general character of the background. Green-colored birds 

 abound in the tropics but are rare elsewhere. The flounder, 

 Rhomboidichthys podas, a bottom-feeding fish, is white under- 

 neath and mottled above. The color pattern of the upper surface 

 can be changed to harmonize with the sea bottom to such an 

 extent as to render the fish practically invisible from above. 

 Some remarkable examples of protective coloration are the 

 seasonal variations such as are found in the ptarmigan, Lagopus 

 lagopus, the otter, Lutra canadensis, the northern fox, Alopex 

 lagopus, and the varying hare, Lepus americanus, whose color in 

 each case is white in winter and varying shades of brown, or gray 

 during the rest of the year. 



Among birds, as a rule the male has far more gorgeous and 

 more conspicuous plumage than the female. The plumage of 

 the male may not have any special significance, but the role of 

 the inconspicuous coloration of the female as a protective adapta- 

 tion during the breeding season seems evident. The young of 

 either sex are protectively colored to an equal degree until sexual 

 maturity when the characteristic adult types of plumage develop. 

 The immediate cause of the two types is an internal secretion 

 produced by the ovary in the female and by the testes in the 

 male. The effect of this secretion in the plumage of the female 

 is the production of a protective type of plumage; in the male 

 the testicular substance seems to produce a result without 

 adaptive meaning. 



Mimicry. — The protective value of coloration is greatly 

 enhanced when the animal possesses in addition a bodily struc- 

 ture bearing a close resemblance to surrounding objects. Such a 

 combination of color and structural resemblances is called 

 mimicry, of which the best examples are found among insects. 

 The dead-leaf butterfly, Kallima inachis, an Asiatic species, 

 when at rest with the wings brought together in a vertical plane 

 over its body, looks remarkably like a dead leaf not only because 



