468 



SCIENCE 



[N. S. Vol. XXXII. No. 823 



illustration, as it is the basic principle upon 

 which all specialized types of markings must 

 be founded, and without which no picturing of 

 detail, however perfect, would be of any value. 

 Tersely stated, practically all animals — birds, 

 mammals, fishes, insects — are darker above, 

 where they receive most light, and graded 

 lighter and lighter toward their shaded under 

 parts, which are paler or white. Thus the 

 natural and inevitable shadow cast by the 

 solid body upon its own under side is " painted 

 off " in the only possible way, and the reflect- 

 ive shadow comes to nearly or perfectly match 

 the dark, but lighted upper surfaces, producing 

 on the whole creature a flat tone, in harmony 

 with its background, upon which may be 

 painted the various detailed devices by which 

 nature seeks to render creatures inconspicu- 

 ous. A series of models, in the form of birds, 

 makes this all-important principle clear. 



In treating the more specialized markings, 

 much emphasis is placed on the importance of 

 highly epitomized semi-distant vistas on the 

 surface of forest-birds, which do not strike the 

 exact focus of the casual eye; an extremely 

 abundant type of marking. Euptive and se- 

 cant markings, interrupting the otherwise con- 

 spicuous profile of the wearers, form an im- 

 portant and frequently encountered class, and 

 are treated at some length, as are iridescence 

 and changeable colors. Indeed, this is one of 

 the most delightful and enlightening chapters 

 in this wholly remarkable book. 



The chapters pertaining to mammals are the 

 ones that will excite the widest discussion, al- 

 though most if not all the contentions of the 

 authors must be vindicated if given a full and 

 honest test. While the fact of the high actin- 

 ity of blue has much to do with the success 

 of many of the photographic illustrations in 

 this chapter, the easily demonstrable fact re- 

 mains that white is the best average match for 

 sky against sky. This has an important bear- 

 ing with nocturnal species with large white 

 marks on their upper surfaces, seen by prey 

 or enemy against the sky. It is also given as 



the reason why all the gulls, terns and other 

 sea birds of the open sky are so largely white: 

 not that they are invisible against the sky, but 

 that white is as near sky-color as anything 

 that can be got, and therefore the best that can 

 be done. 



Fishes come in for an elucidating chapter, 

 as do the reptiles, batrachians and inverte- 

 brates. Here, especially among the insects, 

 we have the most beautiful and convincing 

 evidence of the close study of the authors, 

 and the wondrous results of it. We are 

 shown by what elaborate means, often en- 

 tailing the entire reversal of the basic grada- 

 tion law, nature has managed to overcome the 

 effects of gravity by counter-grading such 

 heavy species of caterpillars as by their weight 

 turn the food-leaves edgewise, and thus them- 

 selves hang " back-down." It is significant, 

 that, the most elaborate adaptation is found 

 during the long senseless and defenceless 

 larval period, when swift motion and keen 

 sight are impossible, and it is certainly among 

 caterpillars that we find the most astounding 

 specific resemblances to exact surroundings. 

 This chapter is one of unbounded interest, and 

 is followed by a discussion of butterflies and 

 moths that is scarcely less exciting. 



While the book teems with specific examples 

 of great charm and covers the whole animal 

 kingdom, and is therefore a complete work in 

 one sense, in another it is truly an introduc- 

 tion, as claimed by the authors. For if the 

 reader be himself open-minded, and, fired by 

 the novelty of the discoveries, try for himself 

 the experiments so graphically described, he 

 will be led irresistibly to a sympathy with the 

 enlightened authors, and there will open to 

 him a whole new realm of discovery — he will, 

 in short, be led back to the delightful field of 

 philosophic and contemplative natural history, 

 which, in these days of minute and technical 

 study of classification and relationships, has 

 been nearly if not quite lost sight of. The 

 greatest value of this unusual book lies notj 

 therefore, in the array of specific fact it con- 



