THE ORIGIN OP SPECIES 119 



of Professor De Vries of Amsterdam, we have come 

 to believe that Nature does make leaps not in- 

 frequently and, it may be, even generally, if only 

 there were a sufficiently large army of detectives avail- 

 able to catch her in the act. De Vries and others 

 have found that some variations appear suddenly and 

 spasmodically (mutations), and that these variations 

 are constant, that is to say, reappear in the offspring 

 generation after generation. Such variations have been 

 termed " mutations," and it must beat once manifest 

 that if mutations be at all frequent in Nature, and have 

 been even more so in past ages, starting-points for Mutation; 

 new races of organisms may have arisen and may 

 now be arising without the need for the long period 

 of time postulated under the natural selection theory. 

 Indeed, as a recent critic has put it, natural selection 

 must have a significance quite different from that 

 attributed to it by Darwin ; for while, according to 

 Darwin, the struggle for existence takes place between 

 individuals, and new species arise by selection of 

 those possessed of variations most likely to aid them 

 in the combat, according to De Vries, fully developed 

 species, produced by a sudden mutation, must come 

 into conflict with those already in existence. One 

 tiling, however, is clear, that the last word has not 

 yet been said on this, the problem par excellence of 

 Biology. 



Science has been defined as the search for unity 

 amid diversity, and even in the course of our brief 

 study of the principles of the science of Biology we 

 have seen this aphorism abundantly exemplified. 

 Both plants and animals, as we have found, possess 

 vitality, both are capable of self-nourishment, and 

 this self-nourishment is effected in both types in 

 fundamentally the same manner, viz., by the assimila- 



