species, Subspecies and Varieties. 167 



the compound Linnean species and to regard the small 

 local or elementary species as subsidiary to them.^ 



But it is clear that this conception of species must 

 result in incomplete investigation and in fallacious con- 

 clusions. For example it is well known that the geo- 

 graphical distribution of species is analogous to that of 

 genera; but it is evident that we should go far astray 

 if we forgot that species like genera were collective enti- 

 ties. The distribution of elementary species, in the geo- 

 graphical region of the Linnean species which they com- 

 pose, is very rarely made the subject of inquiry, yet it 

 is just this point which is of the very greatest signifi- 

 cance as bearing both on the origin and distribution of 

 organisms. According to Jordan every species, as well 

 as every genus, has a geographical center where the 

 distinct component elementary species are most abund- 

 antly represented, growing as they do close together on 

 the same spot, whereas at the circumference of the 

 region inhabited by the species its elements become few 

 and far between.^ 



It is the actual theory of descent itself that would 

 profit most by a proper appreciation of the conception 

 of species. This theory which is recognized in mor- 

 phology, embryology, in systematic work and in com- 

 parative anatomy as the guiding principle of all specu- 

 lation and inquiry has remained almost without influence 

 on experimental biology. At first it raised the hope 

 that science would succeed not only in discovering the 



^ As is very properly done in the classification of parasitic fnnffi 

 where some species are given a higher rank and embrace a certain 

 number of species of a lower rank. See for example Klebahn in 

 Pringsheim's Jahrb. fiir wiss. Botanik, Vol. 34, p. 395. 



^ A. Jordan, De rexistence d'especes vegctalcs aifincs, 1873, pp. 

 4-8. 



