214 UNIVERSITY OF MISSOURI BULLETIN 



physical agents, like the erosive action of water, which are 

 still in operation. Only gradually then has one period of the 

 earth's history passed into the next, and that without any 

 break in the continuity. The effect which this tremendous 

 and inspiring advance in geology had in preparing the way for 

 the establishment of a similar genetic conception in biology 

 cannot be overestimated. Not only did the new interpreta- 

 tion show conclusively that vast periods of time must have 

 elapsed in the formation of the earth's surface a deduction 

 which was of fundamental value to the biologist in furnishing 

 the necessary time for the evolution of the organic world 

 but it also established the presumption that, if natural causa- 

 tion was entirely adequate to explain the origin of the physi- 

 cal structure of the earth, it should prove equally efficient as 

 a means of accounting for the present diversity of organic 

 forms. 



In short, not only had Cuvier's supernatural catastrophism 

 been demolished by Hutton and Lyell, but his type-theory of 

 animate creation, with which it was bound up, was tottering. 

 Accepting the conception of Ray and Linnaeus of the fixity of 

 species, Cuvier, as a result of his studies in comparative anat- 

 omy, distinguished four types in the animal kingdom, each 

 characterized by its own peculiar plan of structure. In his 

 mind, the identity of plan existing throughout a type is the 

 expression of an idea of the Creator, while the variation of 

 the details of structure within the type, with the retention of 

 the fundamental plan, was to him evidence of the Creator's 

 consummate skill. 



It was this view that dominated zoology during the quarter- 

 century between Cuvier and Darwin, although we have seen 

 that it early received a staggering blow at the hands of the 

 geologists. 



Before the storm was to break in its full force in 1859 

 with the publication of the "Origin of Species," the way was 

 further cleared for Darwin by the appearance in England of 



