122 GEORGE HEN SLOW [February 



What, however, I wish to call attention to is, that mimetic 

 resemblances cover a far wider field than that occupied by protective 

 resemblances among insects. In fact, it is equally common in the 

 vegetable kingdom, as it probably is in all classes of animals. 



Protection not ahoays associated with Mimicry. 



Protection is no doubt a benefit, but it does not appear to be 

 always associated with mimicry. It is questionable how far the 

 effect is useful when all the animals of a district are coloured alike, as 

 in a sandy desert ; for not only are the carnivorous animals tawny 

 coloured, but so are their prey, as may be seen in the collection in the 

 entrance hall of the British Museum (Natural History Department), 

 to which might be added a spider and Helix desertorum noticed by the 

 present writer near Cairo. 



It would seem more probable that there has been some general 

 cause in the physical environment. The monochromatic light suggests 

 itself as a cause acting upon all the creatures alike which are subjected 

 to it ; and if the result prove to be advantageous, so much the better 

 for the creatures. That this is the right direction to look for a 

 solution of such mimicry as superficial colouring, appears to be evident 

 from the case of the house-mouse, which Mr. H. Lyster Jameson has 

 described. 1 This author also speaks of " natural selection . . . weeding 

 out unfavourable variations," but he does not appear to have met with 

 any actual cases. He gives a list of thirty-six mice examined, but 

 they range from the common domestic form to the palest-coloured 

 of all. The variations, according to his description, are all in one 

 direction towards a rufous or fulvous gray. In fact, they form a 

 graduated series, but there is no mention of injurious varieties ; indeed, 

 after about one hundred years there are still some 14 per cent of the 

 ordinary mouse-coloured forms still extant. And as the island is fully 

 stocked (a female can give rise to nine at a birth), it is obvious that 

 the sandy-coloured mice are as easily killed off as the others. The 

 fact seems to be that as long as an animal coloured like the ground is 

 at rest it cannot readily be seen, but when it moves there is little 

 difficulty about it. 



That natural selection cannot be a universal cause of mimetic 

 coloration is obvious from the fact that some animals change from 

 brown to white in winter, and many change according to the sur- 

 roundings in which they happen to occur, as in the most familiar case 

 of the chameleon, and a remarkable tick described by Sir J. D. 

 Hooker, who says, speaking of a lizard — " Its throat was mottled with 

 scales of brown and yellow. Three ticks had fastened on it, each of a 

 size covering three or four scales : the first was yellow, corresponding 



1 "On a Probable Case of Protective Coloration in the House-Mouse {Mus musculus, 

 L. )," Journ. Linn. Soc. (Zool.) xxvi. 1898, p. 465. 



