MELANISM AND ALBINISM. 1287 



now know of sexual mimicry ; tlie female, as being the sex which most 

 requires the protection, being the only one which departs from the type. Or, 

 noticing the googr;iphicnl distribution of tliis coloring, the melanic forms 

 occurring altogctlicr in tlic south, wiicn tliey arc at ail limited in tlieir dis- 

 tribution, the albinic forms on the other hand being far more ])revalent in 

 high northern regions, we might expect that when albinism showed itself 

 in polymorphic species (if there were any difference lietween the various 

 generations) it woidd prevail among tliose whici) were boru in the cooler 

 rather tlian in tliose born in the warmer parts of the year, whereas the 

 direct opposite is the ease. If, again, melanism, as largely confined to the 

 south, be looked upon as a product of warm surroundings, we should nat- 

 undly expect it in the later broods emerging in the hot season rather than 

 in the earlier ; whereas in those cases where we know of it as confined at 

 all. it is found in the earlier, cooler part of the year. 



Yet that climatic conditions have something to do with these peculiar 

 colorational features seems almost indubitable. In the first place we may 

 point out that melanism is almost altogether confined to the district south 

 of the latitude of New York ; and that albinism, omittinfj mention of hisrh 

 elevations, is hardly found except north of that same latitude. 



In the second place, it has been shown by several naturalists, notably 

 by Mr. J. A. Allen, that in other de|iartments of the animal kingdom a 

 similar tendency to melanism appears as one passes southward in North 

 America. There is, Allen says, among American birds a general increase 

 in the intensity of color at the southward and "an increase of the extent of 

 the dusky or black markings at the expense of the intervening lighter or 

 white ones, or conversely the reduction in size of white spots and bars." 

 The cases are by no means altogether parallel, but they point in a certain 

 definite and similar direction. This phenomenon, however, should by no 

 means be confounded with that other whicii we observe in butterflies of the 

 high north, where, as compared with the same species further south, there 

 is a blurring of the markings upon the wings and a deepening in their tone, 

 which presents a distinctly melanic effect, an effect which has also been pro- 

 duced artificially by Mr. Edwards in ins experiments upon chrysalids 

 subjected to abnomial cold. Tlie specimens suffer in color and distinct- 

 ness of marking. And here, again, we meet another difficulty ; for how 

 shall we correlate such facts as these with that of the prevalence of albinism 

 in arctic and alpine regions. 



In the third place, these antigenic qualities, which show themselves in 

 a greater and less degree of black markings over the upper surface of the 

 wings in butterflies, are, as far as I am aware, almost entirely confined to 

 temperate regions, where the seasonal climatic differences are at their high- 

 est. Indeed I do not know that a single case of albinism or of melanism 

 properly speaking occurs within the tropics, where the seasonal climatic 



