566 THE POPULAR SCIENCE MONTHLY 



urinations, for instance, of concealing coloration, such as the trans- 

 parency of a group of the supposed mimetics, have gone on, in this 

 group, hand-in-hand with that of unpalatability. Now that we see that 

 all procryptic coloration (except, of course, the facsimile kind, such as 

 that of geometers) produces its effect by making the observer seem to 

 see through the place where the colors are, it follows that actual trans- 

 parency, as in these " mimetics," must, in ever so many situations, be 

 wonderfully potent for obliteration. It is, of course, the only scheme 

 for succeeding equally against both the light and the shadow, tending 

 both to escape showing light against dark backgrounds and dark against 

 light ones. Here are Bates's own remarks about the degree of con- 

 spicuousness of a transparent butterfly. In " A Naturalist on the 

 Amazons," on page 39, he writes : 



Some have wings transparent as glass; one of these clear-wings is especially 

 beautiful, namely, the Hetaera Esmeralda; it has one spot only of opaque 

 coloring on its wings, which is of a violet and rose hue; this is the only part 

 visible when the insect is flying low over dead leaves, in the gloomy shades 

 where alone it is found, and it there looks like the wandering petal of a flower. 6 



As a few hours' experimenting in obliteration by juxtaposition of 

 patterns will prove to any student, the optical laws which govern it are 

 so absolute that one is not surprised to find that the whole world's 

 butterflies have scarcely three different schemes of pattern. The prin- 

 ciple of pattern arrangement in these famous " mimetic " groups (shown 

 in Fig. 6) is out and away the predominant one over the whole globe. If 

 this is the case, is it strange that in each most swarmingly populated 

 seat of butterfly life there prove to be a number of species which, living 

 in the very same station, and with seemingly identical habits, have, in 

 obedience to this great pattern-law, practically identical patterns and 

 form? We see in the ocean, for instance, even mammals wearing the 

 shape and color of fishes ? 



The question, now, is, at most, merely why they have the same sta- 

 tion and habits. 



Let us dwell a moment upon the significance of this finding of the 

 greatest cryptic coloration in the very midst of the so-called mimetics. 

 First we must remember that all men agree that it is only persecution 

 that can have engendered any form at all of protection. It is, as I have 

 said, inconceivable that any forever preyed-on and picked-from race 

 should not have acquired all possible unpalatability. And it is equally 

 inconceivable that any race that either preys or is preyed on should not 

 during the same periods have become, also, as nearly as possible either 

 invisible, or at least unrecognizable as any form of animal life. Such 

 a boon incomparably surpasses any advantage from passing for some 

 other at the best not wholly inedible animal. Therefore one would 



5 The deepest forest shades seem to be, everywhere, the typical home of these 

 transparent species. In Trinidad they bear a popular name that alludes to this 

 characteristic. 



