i io SECRETS OF EARTH AND SEA 



of favoured races in the struggle for existence. But 

 there is always more to be made out difficulties to be 

 removed, new instances to be studied. The classification 

 of the genera of plants and animals, with their included 

 species into larger groups, helps us to state and to 

 remember their actual build and structure, and to survey, 

 as it were, the living world, from the animalcule to the 

 man, or from the microbe to the magnolia tree. Every one 

 interested in natural history should carry in his mind as 

 complete a scheme of the classification of animals and 

 plants as possible. 



The older naturalists held that species were suddenly 

 " created " as they exist, and have propagated their like 

 ever since. Darwin has taught us that the present 

 " species " have developed by a slow process of transforma- 

 tion from preceding species, and these from other pre- 

 decessors, and so on to the remotest geologic ages and 

 the dawn of life. The agents at work have been " variation " 

 that is to say, the response to the never-ceasing variation 

 of the surrounding world or environment and the survival 

 in the struggle for existence of the fittest varieties so 

 produced. 



There is nothing surprising or extraordinary in the 

 existence of variation. The conditions of life and growth 

 are never absolutely identical in two individuals, and the 

 wonder is not that species vary, but that they vary so 

 little. The living substance of animals and plants is an 

 extremely complex chemical substance, ever decomposing 

 and ever being renewed. It is the most "labile" as it is 

 by far the most elaborately built-up chemical body which 

 chemists have ever ventured to imagine. It differs, 

 chemically, not only in every species but in every individual 

 and is incessantly acted upon influenced as we may say 

 by the ever-changing physical and chemical conditions 

 around it. At the same time it has, subject to the 



