A CASE OF PERSISTENT MELANISM. 



H. E. EWING. 



The occurrence of melanism is a phenomenon of wide dis- 

 tribution in nature, being recorded among animals belonging to 

 a great many classes and orders. Our records show that while 

 the occurrences are frequent and are found in species belonging 

 to many of the larger zoological groups, yet the actual numbers 

 of melanic individuals found among the individuals of any one 

 species, in any one region is usually extremely small in com- 

 parison with the total number of normally colored individuals 

 of the same species found in the same region. Because of this 

 rarity of these black-colored individuals the appearance of 

 melanic forms has been very generally regarded as being due to 

 sp'oradic though at times oft-repeated, sporting. Such melanic 

 forms do not usually persist racially. It was Darwin who 

 years ago noted that sports of almost all kinds were ruthlessly 

 eliminated in the struggle for existence; and sporting in the 

 form of melanism apparently has offered no exception to this 

 general rule. 



Perhaps one of the best examples of the racial persistence of 

 melanism is that of the melanic form of the moth, Amphidasys 

 betularia, which existed as a rarity in England some years ago, 

 but which now has replaced the typical form about some of the 

 manufacturing districts. This persistence of melanism has been 

 explained on account of the environment in these districts being 

 changed by the smoke from factories which darkens the vegeta- 

 tion in general, by the killing of lichens and by the depositing 

 of black soot, and in this manner gives an advantage to the 

 melanic forms by making them less conspicuous than the normally 

 colored individuals. 



The Appearance of Melanic Rose Curculios. 

 During the summer of 1913, while in the Willamette Valley in 

 western Oregon, I came across instances of melanism among 



224 



