196 BULLETIN OF THE 



change above described, and indicate the inconstancy of these markings 

 and their unreliability as specific characters. Often, as is well known, 

 these markings in the gulls differ considerably in the two wings of the 

 same bird. 



Although the L. argenlatus has been taken as a general illustra- 

 tion, the same variations with age, or in different individuals, are 

 exhibited by most species of the genus Larus. Generally they 

 are admitted to have no value as specific characters, even by those 

 who in the case of L. argentatus have accorded to them this impor- 

 tance. 



In some of the species of Janco and Pipilo, in Mimus, in numerous 

 species of Dendrceca, in Panda, Mniutilta, etc., there is a similar in- 

 crease with age in the extent of the white markings on the tail, some- 

 times three and sometimes four pairs of feathers being spotted or 

 terminated with white in different specimens of the same species. In 

 short, these variations occur in so many species that they may be looked 

 upon as indicating a general law of variation in color depending upon 

 age, namely, an increase in the purity or intensity of the general color, 

 and an increase in the size of the wing and tail markings, for a time, 

 witl i age. 



After complete maturity is attained there is, however, unquestionable 

 evidence of a decline in color, which in many cases, and especially in 

 bright-colored species, is quite marked. So general is such a decline 

 in other groups of the animal kingdom that a citation of evidence on 

 this point seems wholly needless. Yet in birds, in numerous instances, 

 it is scarcely appreciable, and doubtless is in most species too slight to 

 be readily traced. This obscurity may result, however, more from an 

 absence of favorable conditions for such a decline to be recognized 

 than from its real absence. It can hardly be doubted, in fact, that a 

 share of the color variation seen in mature birds is attributable to this 

 cause. It is well known that young mammals in their first pelage are, 

 as a general rule, much darker colored than the adults of the same spe- 

 cies. At a later period the color fades more slowly, but in old 

 age the hair often beconi"- more or less gray, the blanching being in 

 some cases very marked. Nearly all birds are also darker in their nest- 

 ling and immature stages of plumage than alter they arrive at maturity, 

 especially if in the adult stage the plumage is light colored ; and it is 

 more than probable, and in some cases certain, that the decline in color 



