QUANTITATIVE METHOD AND PRIMORDIA 27 



§ 31.— THE USE OF THE QUANTITATIVE METHOD 

 IN THE DESCRIPTION AND CLASSIFICATION OF 

 SPECIES. — LINN^US adopted a classification of the vege- 

 table kingdom founded to a large extent on the number of 

 stamens and pistils. For instance, the classes I. to X. of the 

 Linnaean system included plants with one, two . . . ten 

 stamens. Each class was divided in its turn into orders 

 according to the number of pistils, etc. This system has been 

 severely criticized and even violently attacked. It is certainly 

 unnatural, but botanists have overlooked the creative power 

 of the principle upon which it is based. 



In the description of the mammalia we use the dental 

 formula which indicates the number of incisors, canines, etc., 

 in each species. 



The ichthyologists find important specific characteristics in 

 the number of dorsal and anal fins, in the number of their rays 

 and also in the number of scales. 



In the description of articulate animals much importance is 

 attached to the number of segments (somites, articles) of the 

 body, the legs, etc., the number of eyes, and even the number 

 of certain kinds of hairs. LATREILLE is the author of a 

 classification of the coleoptera based upon the number of seg- 

 ments of the tarses (Pentamera, Heteromera, Tetramera, etc.) 

 which has rendered and is still rendering good services. 



The mosses have been classified according to the number of 

 teeth of the peristome. 



One of the first applications of the quantitative method has 

 been the measurement of the facial angle. An interesting 

 application is the so-called bertillonage. This is the description 

 of a person by means of a combination of figures, obtained by 

 measuring certain properties. 



We see from the above examples that the quantitative 

 method has already been used to a large extent. 



Most biologists, however, look upon the use of quantitative 

 data as being something artificial. They overlook their 

 PRACTICAL importance for the identification and the exact 

 description of living beings — in general, for the exact descrip- 

 tion and comparison of biological facts — whatever may be their 

 value as a base of classification and independently of any 

 theory. 



§ 32.— THE MEASUREMENT OF VARIABLE PRO- 

 PERTIES. BIOMETRY. — The use of the quantitative 

 method has been hitherto almost entirely confined to the 

 measurement (including counting) of properties which are in- 

 variable or almost invariable. Its application is more difficult 

 when we want to investigate variable properties. Every 



