158 THE WORLD OF LIFE CHAP. 



white band across the wings in this order of insects (Fig. 23). 

 This strange and most unusual modification of an inoffensive 

 insect, so as closely to resemble one of another order which is 

 protected by a dangerous sting, can be explained in no other 

 way than through the advantage derived by the harmless 

 beetle by being mistaken for the wasp. Of course, this 

 change is the result of a very long series of slight modifica- 

 tions of the beetle, each bringing it a little nearer to the 

 wasp, a series extending probably through thousands or even 

 millions of generations. 1 



Recognition- Marks 



But though the subject of " mimicry " involves problems 

 of extreme complexity and interest, and has therefore 

 attracted the attention of numerous students, yet it is almost 

 entirely confined to the insect world, and, taken as a whole, 

 is not nearly so important a factor in the development of 

 the great world of life as the class of " recognition "-colours 

 of which I will now give a short account 



My attention was first directed to this subject during my 

 visit to south Celebes in 1856-57, where, during about six 

 months' collecting, I obtained the unusual number of fifteen 

 different birds of prey, of which the majority were of the 

 hawk sub-family. While skinning and preserving these birds, 

 and after my return home while determining the species, 

 I could not help observing in many of them the varied 

 and beautiful markings of the tail-feathers, by means of 

 white spots or bands on all the feathers except the middle 

 pair. The result was that when the tail was expanded 

 during flight, it was seen to be marked very conspicuously 

 by white bands, sometimes across the middle of the tail, 

 sometimes at the end, sometimes with one band, sometimes 

 with two or even three, so that the species were easily dis- 

 tinguished by this one character. But the chief peculiarity 



1 Other cases are given in my Darwinism ; but those who wish to under- 

 stand the whole problem and what an important part it plays in nature should 

 read Professor Poulton's elaborate papers in the Transactions of the Entomological 

 Society of London for the years 1902 and 1908, together with those of Dr. F. A. 

 Dixey and other writers. There is also a very good article by Mr. R. Shelford, 

 on mimetic insects from Borneo, and as these are illustrated by coloured plates 

 and deal with cases of the same nature as the one here given, they are very 

 instructive. (See Proceedings of the Zoological Society of London, Nov. 4, 1902.) 



