176 Charles Darwin. 



arity may appear. We may call it a monstrosity, a 

 freak, or an accident, but if the conditions are nor- 

 mal, the chances are that it will be perpetuated to 

 some extent, while if they are extremely favourable 

 it may be transmitted indefinitely. There is no con- 

 troverting this ; it is a simple fact understood by 

 everyone. Darwin recognised it, and accumulated 

 a vast amount of testimony showing its possibilities 

 in all ranks of life ; and seeing that varieties could 

 be produced in domestic animals and plants, he laid 

 down the theory that almost the same selection and 

 discrimination are taking place in nature ; the ten- 

 dency being to perpetuate certain features, which in 

 time become so prominent that they assume the 

 dignity of varieties. As an illustration I cite an 

 instance of my own observation. We have seen that 

 man produces the trotter by weeding out those 

 which vary from this type ; now let us glance at 

 nature and note how animals may gradually assume 

 a like appearance by selection. Several years ago 

 I was drifting along on the edge of the Sargasso 

 Sea, when my attention was attracted to the re- 

 markable fauna of the weed. Here was the curious 

 fish, Antennarius, lying prone upon the weed near its 

 nest — a ball of sargassum. Had I not been familiar 

 with the little creature it would have escaped my 

 notice, as its colouring was identical with that of its 

 surroundings : not a fanciful resemblance but one 

 in fact ; the very tints and hues being imitated as if 

 the fronds and leaves of the sargassum had been 

 photographed on the sides of this curious mimic. 

 The crabs all partook of the same protective favour, 



