560 Mr. A. H. Thayer ooi 



form in widely separated orders, plainly accompanying 

 common environment and habits. The Salmon's silver, 

 grading upward into dusky, and downward to jDurest 

 white, is identical with that of countless fish in many 

 groups, and no one doubts that environment and habits 

 are the cause. Among birds, Embcriza miliaria, Anthus 

 pratcnsis, Alaiula arvcnsis, and Alauda arhorca are four 

 species of three genera for all four of wliich one minutest 

 colour-and-pattern-description would almost suffice ; and 

 the same colour-scheme and pattern with slight varia- 

 tions is found on a great many other species throughout 

 the world, both of Passcrcs and even Scolopacidic and 

 GalliiicV, telling plainly of life on the ground amidst 

 grasses. Among the ScoloimcidiV , many females and young 

 of the AnatidiV, and the Laridtv, Nature betrays, in the 

 main, great lack of variety in design, easily accounted for 

 by the lack of variety in the aspect of the environment. 

 In a broad survey of the animal kingdom we perceive that 

 everywhere the degree of colour-and-pattern difference 

 between different members of an order, family, or genus 

 keeps pace with the degree of variation in their environ- 

 ment's aspect. 



Why may not the circumstances of a group of butterflies 

 furnish them similar needs to wear a common livery, even 

 if we cannot see the reason ? Might they not tend also 

 to have their flavour similarly affected by similar food ? 

 The Spruce Grouse (CanacMtcs canadensis) is saturated 

 with spruce flavour, and the world is full of such cases. 

 Even the amazing similarity between members of these 

 groups is no proof they may not, for reasons which we 

 have not discovered, profit each by exactly the same form 

 of concealing-coloration. It should be borne in mind that 

 it is not afloivcr that those mimics evidently represent, 

 but a certain combination of the flower's aspect with that 

 of its surroundings. Hence there may be one best way 

 to render this. Butterflies on wing are conspicuous, but 

 are wonderfully protected by their jerky flight, which is 

 completed by their wings Ijeing so large as necessarily 

 to throw the body up and down at every movement. 

 This latter advantage, attainable by no other conceivable 

 means, may be a great factor in the whole matter. In 

 flight they are doubtless practically safe, i. e. too trouble- 

 some a quarry to be seriously decimated. I send, for 

 Professor Poulton to exhibit, photographs of a number 



