376 Evolution by Jumps 



have a series of intergrading forms. There are either twelve 

 ribs or there are more, or fewer; the cow has horns or she 

 has not. Each numerical value stands distinct from the 

 next. Stature or any other dimension might fluctuate by 

 " imperceptible " degrees. Physiological characters may 

 fluctuate more or less. Things that we can count, however, 

 are always in a discontinuous series. Many of the cases are 

 undoubtedly monstrosities or morbid conditions, such as the 

 growing together of parts that are normally separate, or the 

 development of supernumerary legs in a calf. Many others, 

 however, represent discontinuities that cannot be considered 

 *' freaks " or monsters. 



Studies made among many species of plants and animals 

 showed these discontinuous numerical or meristic variations 

 to be very common; and in many cases the variation from 

 the normal was found to be transmitted to offspring — the 

 broad-fingered condition in man, for example, wherein the 

 fingers are found to lack one joint (see Fig. 56) . 



Another type of discontinuous variation illustrated in 

 Bateson's collection is represented by the transformation of 

 an organ into another homologous one. Among flowers, for 

 example, leaflike structures sometimes appear in place of 

 the stamens or carpels, as in the formation of " double '* 

 roses. Among crabs one sometimes finds an eye replaced by 

 an antenna. Skin glands sometimes take on the structure of 

 milk glands. Many other abnormalities are reported, indi- 

 cating the development of a specialized organ into one less 

 specialized — and sometimes a divergence in the opposite 

 direction. 



The Origin of the New 



At the end of the Nineteenth Century the discussion 

 among the evolutionists centered around the evidence for 



(i) the origin of variations that might serve as the 

 basis for selection; and around the evidence for 



(2) the effectiveness of natural selection. 



