2$6 EVOLUTION OF TO-DAY. 



organisms, of whose workings we know nothing. 

 Mivart, after marshalling in battle array all of the 

 possible objections against natural selection, comes 

 to the conclusion that it is a law of nature of lit- 

 tle importance, and playing only a secondary and 

 very subordinate part. He advances in its place a 

 theory, of which he is not, indeed, the originator, 

 though he is its chief exponent. Owen, Kolliker, 

 the Duke of Argyle, and other well-known scientists, 

 share his views. He thinks species have arisen sud- 

 denly, by extraordinary births and not by slow modi- 

 fication. He grants that a very great amount of 

 variation may occur in any species: experiments 

 with domestic animals prove this too conclusively for 

 denial. But he thinks that these variations are not 

 indefinite and not unlimited. They are, in his view, 

 always in certain directions, and always confined 

 within certain bounds. By variation alone, he says, 

 no new species ever arise. By ordinary variation 

 many cases may be developed, differing from each 

 other in very marked degrees, but they form simple 

 varieties, are always within the bounds of the species, 

 and never become so different as to be sterile when 

 crossed. Mivart does not believe, therefore, that 

 varieties are incipient species. Species arise by 

 sudden extraordinary births. An animal is born 

 which differs from its parents, in certain respects, so 

 much that it is from the first a new species. It is a 

 " new chord in nature." As to the laws regulating 

 such births, Mr. Mivart acknowledges complete igno- 

 rance, but he thinks that enough strange births are 

 known to indicate them to be the factor sought. 



