188 The Mechanism of Evolution in Leptinotaesa 



whereas it has generally been the opinion of biologists that the essential differ- 

 ences between specific living substances are of a qualitative nature. This is 

 important because, if true, quantitative accumulations ought in the end to pro- 

 duce diversity of the kind spoken of as qualitative differences. It raises the 

 question, can quantitative accumulations in the parts produce resultant qualita- 

 tive differences of the whole ? This is a problem well adapted to exact experi- 

 mental test ; that is, can the accentuation of an attribute produce a change in 

 the quality of which the attribute is a mass manifestation ? 



The quantitative concept implies change in the amount of something, with the 

 retention of the same spatial relations ; the qualitative implies the establishment 

 of different relations from those hitherto existing. This concept can not be ap- 

 plied at present to the conditioning factors in the germinal material, but it is 

 possible to determine whether the variations are mere plus or minus differences 

 in quantity or material or activities, without reference to spatial relations, or 

 whether the common fluctuations are small differences in the spatial and other 

 relations of the character in question. 



The discontinuity which species in nature show is, by this conception, ex- 

 tended to the characters of which organisms are supposed to be composed; 

 whether there is discontinuity between the unit-characters became, therefore, a 

 problem for solution. Because many species show in nature a certain discon- 

 tinuity in that there are no intergrades, it seems more reasonable to some 

 (Bateson, De Vries) that they arose in that way and that there have never been 

 intergrades, while the fact that there are in nature species groups with inter- 

 grades seems to others evidence to maintain that all species groups have arisen 

 through the gradual separation of groups and the extinction of intergrades. In 

 the same way the variations are far too often classed as continuous whenever 

 intergrades can be foimd and as discontinuous where such are wanting. As a 

 matter of fact, the existence or nonexistence of visible intergrades is of no 

 importance; only intergrading gametic conditions as determined by breeding- 

 tests are of interest. However, in nature the variation conditions in a popula- 

 tion are always confused, and mere somatic aberrations, rare chance reconstitu- 

 tions, and true transmutative variations may easily be confounded and classed 

 as mutations and as discontinuous in character. 



Another point upon which there is difference of opinion is raised by the asser- 

 tion that the only safe basis of study in variation is the " unit-character," mean- 

 ing thereby some attributes which, as far as is known is not divisible in the 

 organisms, but is present or absent in its entirety. To some these attributes 

 represent the initial unit of structure and activity in the organism, and are, 

 therefore, the only basis from which to proceed in the analysis of organic phe- 

 nomena, while others hold that the problems must be considered from the point of 

 view of the whole. Naturally these two bodies of workers will arrive at quite 

 different end-results, and not infrequently will fail to appreciate the results 

 obtained by each other. This situation results, naturally, from the difference in 

 the initial philosophical starting-point, and if one's conception of organisms is 

 of the unit-character mosaic variety, unit-characters of necessity become 

 supremely important in the constitution, evolution, and activities of organisms, 

 while if the individual is considered as entity, then all too often that point of 

 view considers only the sum total effect produced on his senses by the particular 

 organism, and his statement of the conditions becomes a sort of impressionistic 



