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Recent Literature. lAnril 



or in part to optical effects, due to mechanical structure, as in the case of 

 iridescent feathers, scales, etc., by which the light rays are scattered, dif- 

 fracted, or unequally refracted; in such cases, however, a background of 

 dark pigment is necessary for the display of the metallic lustre. A 

 variety of pigments has been found and chemically analysed, by which 

 it is found that the same color, even in allied forms, is not always due to 

 the same pigment. "The brown colour of birds is chiefly due not to one 

 pigment, but to two apparently distinct pigments, which give different 

 chemical reactions." The green color of the Turacou is due to an 

 entirely different pigment from that which causes the green color in 

 Parrots. Thus the same effect is often produced by quite different pig- 

 ments. Again, differently colored animals have the same pigment, as in 

 the case of the very differently colored sexes in the Parrots of the genus 

 Eclectus, the color difference being due to a difference in the structure of 

 the feathers, the males in these Parrots being colored green and the 

 females red. 



Color is believed to be "a normal product of organization, entirely 

 independent of utility" ; yet there is good evidence that " 'coloration' bears 

 often a distinct relation to the needs of the animal," and may therefore be 

 modified by 'natural selection,' using this term in its broadest sense. On 

 the other hand, it is quite evident that coloration is not always in harmony 

 with the mode of life of the animal, while often 'complex markings' are 

 so placed as to be of no possible use to the animal possessing them. It is 

 hence frequently impossible to advance any reasonable hypothesis to 

 account for their presence. Hence Mr. Beddard freely admits that the 

 "action of natural selection" in producing color changes is limited. He 

 also calls attention to the comparative constancy of color and color mark- 

 ings throughout whole genera and even families, and also that the same 

 plan of coloration is often repeated in very distantly related groups. 

 This fact is sometimes explained on the ground of mimicry, but in many 

 cases such an explanation is beyond supposition. 



In some instances there is apparently some relation between coloration 

 and structure of the underlying parts of the organism, but the cases where 

 this is obvious, or where some better explanation may not be suggested, 

 are very few: the agreement is, we believe, more a matter of chance 

 coincidence than one of any deeper relation. 



In discussing changes of color during the lifetime of the individual, Mr. 

 Beddard points out various flaws in the reasoning of Weismann and Poul- 

 ton on the subject, but leaves much unsaid that may be urged in oppo- 

 sition to their views. Lack of space, however, forbids entering upon the 

 subject in this connection. 



Mr. Beddard, we are glad to see, is willing to grant that the influence of 

 an animal's surroundings may exercise a direct influence upon its 

 coloration without the intervention of .the agency of 'natural selection.' 

 Under this head are verv properly considered the seasonal changes of 

 many Arctic animals. 



