THE NATURE OF SPECIES 



used later (de Vries, 1901) in a nearly opposite sense — 

 that is, to denote sudden variations, or sports. 



Herbert Spencer remarked: "Those who reject the theory 

 of evolution as not adequately supported by the facts accept 

 instead a theory which is supported by no facts at all." The 

 development of specific differences — differences marking 

 species — by gradual change from generation to generation 

 has been well established by collecting fossils from successive 



oo oO 



Flat Arched Ridged Conical 



M. Corbovis 

 Fig. 2. — Sea-urchins formed in the English Chalk. 



layers in a series of deposits and comparing each fossil with 

 its predecessors and successors. 



The sea-urchins in the English Chalk that belong to the 

 extinct genus Mi cr aster (Fig. 1) provide a convenient illus- 

 tration of the evidence thus obtained as to the actuality and 

 nature of evolution. This sea-urchin is a common and well- 

 preserved fossil, and it shows variations that might be 

 regarded as distinctive of two or more species. The late 

 Dr. A. W. Rowe, of Margate,"" collected 2,000 specimens of 

 M/craster and carefully recorded for each specimen its level 

 in the Chalk. They show gradual variations (Fig. 2) as 

 they are followed upward through the Chalk. They are of 

 four chief shapes, all of which have come from the earlier 



^ Quart. Jour. Geol. Soc, Vol. 55, 1899, pp. 494-547, pis. 35-9. 



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