COLORING AND LATITUDE. 1767 



under surface of the hind wings of a clear canary yellow, and what few spots 

 they possess are clustered into sharply defined niarkino-s next tiic niarsin ; 

 these features predominate until we arrive at tiie middle states, wlujn a 

 change begins ; and on reaching Labrador we find the opposite extreme, a 

 ground color of greenish yellow completely flecked with atoms of brown, 

 giving the wing a grimy appearance ; while the marginal markings are 

 simply more densely clustered atoms, forming spots which gradually pass 

 into tlie general dinginess of the wing. 



This loss of purity and greater or less suflPusion of markings is char- 

 acteristic of northern and alpine forms, and is in perfect accord with another 

 phenomenon, the appearance 6f those varieties or sports which are called 

 examples of suffusion. Although they frequently seem very unlike the 

 normal form, a little study always suflSces to show to what species they be- 

 long. This disguise is produced, as already stated in the Excursus devoted 

 to that subject, by the blending of certain colors, especially of black, white, 

 or silvery tints, which normally occur at distinct parts of the wing. Now 

 these suftusions have been known almost exclusively from the temperate 

 regions, and have been artificially produced by subjecting chrysalids to un- 

 usual cold. A large number have been recorded in Europe, where they 

 are commonest in the alpine districts of Switzerland. 



These general changes of prevailing tints among butterflies from the 

 tropics northward are perhaps less striking because so gradual, and seem 

 fairly connected with physical conditions ; color is dependent upon light, 

 and of course the greatest intensity and duration of light is in the tropics ; 

 the two phenomena are completely parallel. It is, however, harder to 

 understand a very curious sport in one of our butterflies, which is known 

 to have originated within recent years. There are a very few butterflies 

 common to this country and Europe ; and not a few entomologists have 

 attempted to find some difference between representatives from either con- 

 tinent, thus far without real success. Within a few years the cabbage 

 butterfly, as we have seen, was accidently introduced from Europe, and 

 has now spread widely ; nor does any difference exist between European 

 and ordinary American examples of this insect. But there suddenly ap- 

 peared in this country a variety unknown to Europe, or, if known, exces- 

 sively rare, in which the normal chalky white, which forms almost the only 

 color of the upper surface of the wings, is replaced by a pale sulplmr tint ; 

 probably few of our entomologists have not seen this variety, although from 

 its resemblance on the wing to our commonest of butterflies, the clouded 

 sulphur, it would ordinarily escape observation. 



Table of the species of Lerema, based on the imayo. 



Hind winjjs beneatb warm, ferrU!,'inous brown, outer margin enlivened with a bluish or lila- 

 ceous bloom ; clasps of male abdominal appendages excised above just before the tip — acciiis. 



Hind wings beneath cold, dark brown, the outer margin with a hoary bloom ; clasps of male ab- 

 dominal appendages excised far before the tip hlanna. 



