140 MEANING OF THE SYSTEM. 



sion and to the state of scientific knowledge. la this sense Goethe 

 appropriately calls a natural system a contradictory expression. 



In establishing systems, that which comes into contemplation 

 consists of the individual forms which are the objects of observation. 

 Every systematic conception, from that of the species to that of the 

 type, depends upon the bringing together of similiar properties, and 

 is an abstraction of the human mind. 



Species. The great majority of investigators, till very recently, 

 were agreed in looking upon the species as an independently created 

 unit with special properties which were retained in propagation, and 

 were really contented with the fundamental idea in Linnaeus' defini- 

 tion of species : Tot numeramus species quot db initio creavit in- 

 finitum ens." This view also accorded with a dogma prevalent in 

 Geology, according to which the flora and fauna of the successive 

 periods of the earth's history were completely isolated, being created 

 afresh at the beginning and destroyed by a vast catastrophe at the 

 end of each period. It was supposed that no living thing could be 

 preserved through one of these catastrophes from one period into the 

 next ; that every species of animal and plant was specially created 

 with definite characters, which it retained unchanged until it was 

 destroyed. This idea was confirmed by the difference between the 

 fossil remains of Vertebrates (Cuvier) and Molluscs (Lamarck), and 

 the living forms of these types. 



As a matter of fact, however, neither in the animal nor in the 

 vegetable kingdom do offspring resemble exactly the parent forms 

 from which they have originated, but present differences more or 

 less considerable, so that the idea of absolute identity must be 

 removed from our definition of species, and agreement in the most 

 essential particulars introduced in its place. The species would ac- 

 cordingly, in close agreement with Cuvier's definition, include all 

 living forms which have the most essential properties in common, are 

 descended from one another, and produce fruit ful descendants. 



All the facts of natural life, however, can by no means be arranged 

 agreeably to this conception, which has for a fundamental principle 

 that all essential peculiarities must be preserved unaltered by repro- 

 duction through all time. The great difficulties in defining species 

 which occur in practice, and which prevent a sharp line being 

 drawn between species and variety, indicate the insufficiency of 

 the conception. 



Varieties. Individuals belonging to the same species do not 

 resemble each other in all particulars, but present differences which, 



