104 FACTORS OF EVOLUTION 



(' 

 pointed out, the characters which visibly differentiate species a/e 

 not as a rule capital facts in the constitution of vital organs, put 

 more often they are just those features which seem to us useless 

 and trivial. . . . These differences are often complex and are 

 strikingly constant, but their utility is in almost every case 

 problematical." 



Lastly, W. Bateson (loc. cit., p. 5) refers to another difficulty 

 which is common for the theory of Lamarck as well as for that 

 of Darwin. He says : — " In the way of both solutions there is 

 one cardinal difficulty which in its most general form may be 

 thus expressed. According to both theories specific diversity of 

 form is consequent upon diversity of environment, and diversity of 

 environment is thus the ultimate measure of diversity of specific 

 form. Here then we meet the difficulty that diverse environments 

 often shade into each other insensibly and form a continuous 

 series, whereas the Specific Forms of life which are subject to 

 them on the whole form a Discontinuous Series . . . forms which 

 are apparently identical live under conditions which are apparently 

 very different ; while species which though closely allied are 

 constantly distinct are found under conditions which are apparently 

 the same." On a subsequent page (p. 17) the same writer says, 

 " The first question which the Study of Variation may be expected 

 to answer, relates to the origin of that Discontinuity of which 

 Species is the objective expression. Such Discontinuity is not 

 in the environment ; may it not, then, be in the living matter 

 itself ? " 



Fundamental difficulties of this kind de Vries claims to meet 

 and answer by his ' Mutation theory,' the details of which he has 

 recently published after many years of laborious but most fruitful 

 research. Some of the old examples may, however, first be cited 

 of this more or less sudden cropping up of 'sports' or actual 

 new species, before dwelling further on the views put forward by 

 de Vries. 



One of the most remarkable of known instances of per saltum 

 development is the fact recorded by Darwin ' that on five separate 

 occasions what Sclater has pronounced to be a distinct species 

 of Peacock — the "black shouldered kind," or Pavo nigripennis — 

 has appeared suddenly in a stock of common or pied peacocks, and 

 in two of the cases (that is, in the flocks of Sir J. Trevelyan and 



' "Animals and Plants under Domestication," vol. i., p. 322. 



