64 Mutability and Indiz'idiial Variation. 



Especially zvith Regard to Discontinuity in the Origin 

 of Species. The special part of this book consists of an 

 exhaustive catalogue of instances of variations in num- 

 ber, or so-called meristic variations, in the animal king- 

 dom. Variations and mutations in the number of verte- 

 brae, of fingers, of joints of the tarsus, etc., are set 

 forth, and are included under the term discontinuous 

 variations.^ The general part is devoted to a criticjue of 

 the modern theory of evolution. The theory of descent 

 has, according to Bateson^ not merely to account for 

 the kinship of organisms. This point is already granted. 

 But it also has to explain the differences between indi- 

 vidual forms and, with regard to this point, Bateson 

 asserts with perfect right that the species alive at the 

 present day are sharply and completely separated from 

 one another, and that transitions between them either 

 do not occur at all, or at most, very seldom. Existing 

 species form a discontinuous series. The theory of 

 descent, therefore, has to account not only for their 

 relationship, but also for this discontinuity.^ The latter 

 forms one of the weak points in the current theory of 

 selection. For according to this theory, the series of 

 ancestors of any given organism must be a continuous 

 one, seeing that the only differences between parents and 

 offspring are of the so-called individual or fluctuating 

 kind. Whence then arise the gaps which now separate 

 species from their nearest allies? 



The usual answer that is given is to point to the ex- 

 istence of numerous intermediate forms These however 

 are not transitional forms, but independent types, namely 



* See especially pp. 568 and 571 ; also pp. 15, 6t, etc. The argu- 

 ment of Duncker (Biol. Ccnfralblatt. 1899, p. 372)^ is therefore not 

 really directed against Bateson's use of the term discontinuous. 



^ See pp. 5, 17, etc. 



