1716 THE BUTTERFLIES OF NEW ENGLAND. 



When by a different mode of life or by being confronted with new 

 emergencies or by any other change in the environment, a chance has 

 offered for new structural adaptations, then has been the most favorable 

 time in a given type for a more or less marked divergence in pigmental 

 distribution from others of its brethren which are following a different 

 track and trying another chance in life. So it comes about that color and 

 color patterns have assumed a definite relation to genera and tribes and 

 sometimes even to subfamilies, the most marked case of the latter, per- 

 haps, being the prevailing subdued brown monochrome of the upper sur- 

 face of the wings of the Satyrinae and the prevalence on their under 

 surface of ocellated markings. 



Other examples which run through whole tribes or prevail in them are 

 seen in the Vanessidi with the marmorate markings of their under surface ; 

 the Argynnidi with their large silvery nacreous or greenish nacreous spots 

 in concentric rows on the same surface, or the fulvous upper surface 

 blocked with black ; the Theclidi with their upper surface monochrome or 

 with only two colors displayed in masses and the markings of the under 

 surface transversely linear and most delicate ; the Lycaenidi with their 

 affection for pale or silvery blue and their markings beneath mostly in tiny 

 circlets, lunules or points arranged transversely. So, too, the orange and 

 yellow of the Rhodoceridi, the white of the Pieridi and the black margined 

 fulvous of the Pamphilidi are cases in point. To enumerate or to merely 

 begin to enumerate the genera were a wearisome task. The tessellated 

 Hesperia is a sufficient example. 



Since in a large number, perhaps the vast majority, of cases, the pattern 

 of the under surface of the wings is protective and is markedly similar in 

 a great variety of allied forms (witness the Anthocharidi) , this pattern 

 must have been gained at a remote epoch by the common ancestors of all 

 so marked ; whence it follows that this form of mimiciy is of high an- 

 tiquity and has been a supple means in the hands of nature of originating 

 new forms. But on the other hand, parastatic mimicry, except in a few 

 tropical cases like the Leptalids, must be of comparatively recent origin 

 and cannot liave been of any special service in the origination of new types. 

 For not only do we often find it confined to a single sex of a species, but 

 the species concerned sometimes departs so vridely from the pattern of its 

 fellows as altogether to set at defiance the laws of colorational pattern 

 which otherwise hold good everywhere. If parastatic mimicry had ob- 

 tained in the distant past and had been the means of originating new fomrs, it 

 would have revolutionized the world of butterflies and have rendered far 

 more complicated than now the explanation of their colorational patterns. 

 We are, perhaps, eye-witnesses of the initiation of a new departure in the 

 selective work of nature ; a departure which the geologically speaking 

 recent development of insectivorous birds has rendered necessary to the 

 preservation of butterfly life. 



