INTRODUCTORY 15 



immutability of species which Linnd briefly characterized in these 

 words : ' Species tot sunt, quot formse ab initio creates sunt,' 

 'there are just so many species as there were forms created in the 

 beginning.' It is here clearly implied, that species as we know them 

 have been as they are from all time, that, therefore, they exist in 

 nature as such and unchangeably, and have not been merely read into 

 nature by man. 



This view, though we cannot now regard it as correct, was 

 undoubtedly reasonable, and thoroughly in accordance with the spirit 

 of the time ; it was congruent with the knowledge, and above all with 

 the scientific endeavours of the age. In the eighteenth century there 

 was danger that all outlook on nature as a whole would be lost — 

 smothered under the enormous mass of isolated facts, and especially 

 under the inundation of diverse animal and plant forms which were 

 continually being recognized. It must therefore have been regarded 

 as a real deliverance, when Linn^ reduced this chaos of forms to 

 a clearly ordered system, and relegated each form to its proper place 

 and value in relation to the whole. How, indeed, could the great 

 systematist have performed his task at all, if he had not been able to 

 work with definite and sharply circumscribed groups of forms, if he 

 had not been able to regard at least the lowest elements of his system, 

 the species, as fixed and definite types ? On the other hand, Linnd was 

 much too shrewd an observer not to entertain, in the course of his 

 long life, and under the influence of the continually accumulating 

 material, doubts as to the correctness of his assumption of the fixity 

 and absoluteness of his species. He discovered from his own 

 experience, what is fully borne out by ours, that it is easy enough to 

 define a species when there are only a few specimens of a form to deal 

 with, but that the difficulty increases in proportion to the number 

 and to the diversity of habitat of those that are to be brought under 

 one category. In the last edition of the Systenta NaturcB we find very 

 noteworthy passages in which Linne wonders whether, after all, a 

 species may not change, and in the course of time diverge into 

 varieties, and so forth. Of these doubts no notice was taken at the 

 time ; the accepted doctrine of the fixity of species was held to and 

 even raised to the rank of a scientific dogma. Georges Cuvier, the 

 great disciple of the Stuttgart ' Karlschule,' accentuated the doctrine 

 still further by his establishment of animal-types, the largest groups 

 of forms in the animal kingdom within which a definite and funda- 

 mentally distinct plan of architecture prevails. His four types. 

 Vertebrates, Molluscs, Articulate and Radiate animals, furnished a 

 further corroboration of the absolute nature of species, since they 



