326 GEORG DUNCKER [November 



That elementary complex of individuals, which is usually the 

 starting-point for zoological and botanical investigations, is the species. 

 More or less exclusively, all biological, systematic, and anatomical 

 results are referred to this. But the species is by no means an 

 elementary group ; even if we omit its systematic sub-groups, the 

 variety and the race, we find it empirically to be composed of in- 

 dividuals which are separated by space and time, and are allied to 

 each other in different degrees of kinship. In those individuals of 

 the same species there regularly occur morphological differentiations 

 of their common characters, caused by constitutional factors (conditions 

 of sex, stage of development) as well as by the sum total of recognis- 

 able external conditions of life (locality, geological formation, climate, 

 food, etc.). Keally elementary complexes of individuals, co ipso 

 coherent, are only those of which the morphological qualities have 

 not been differentiated by any of the factors just enumerated. But 

 even in such a " form-unit," as I have called it [7], we find on 

 investigating the distinctive characters that there are individual 

 differences. 



Therefore the species is not elemental, a conclusion strengthened 

 by the difficulty (bordering upon impossibility) of definition. It splits 

 up in numerous variable form-units, produced by different factors, 

 which frequently may be united into races or varieties. Each form- 

 unit is a sum of more or less different individuals, the characters of 

 which change in the course of development, that is, in time, but 

 appear constant at a given moment, so that it is not justifiable to 

 speak of varying or non-varying individuals. On the other hand, 

 groups of individuals are variable in every moment of their existence 

 and in each of their characters. Therefore the fact of variation is to 

 be seen only in the characters of groups of individuals, and to be 

 investigated only in these. 



The exact study of variation affords a better understanding of the 

 systematic relations between groups of individuals ; it is a means of 

 distinguishing pathological from normal states ; but it owes its highest 

 importance to its bearing on the theoretical explanation of the re- 

 lations between organic individuals, i.e. in regard to heredity and 

 evolution. 



The objects of an investigation on variability are the characters of 

 a complex of individuals and, according to the laws of induction, at 

 first of the most primitive complex, the form-unit. The aim of this 

 investigation is twofold ; on the one hand qualitative, to discover the 

 real individual differences in these characters, which we may call the 

 variants ; on the other, quantitative, to discover the relative frequencies 

 of the single variants of each character determined. 



The principal difference between a character of a single individual 

 and one of a complex of individuals, therefore, consists in the possibility 

 of expressing the former by a single variant, while the latter requires 



