ILLUSTRATIVE OF NATURAL SELECTION. 163 



minifera," he states that "there is not a single specimen 

 of plant or animal of which the range of variation has 

 been studied by the collocation and comparison of so 

 large a number of specimens as have passed under the 

 review of Messrs. Williamson) Parker, Rupert Jones, and 

 myself, in our studies of the types of this group ; " and 

 the result of this extended comparison of specimens 

 is stated to be, " The range of variation is so great 

 among the Foraminifera as to include not merely those 

 differential characters ivhicli have been usually accounted 

 SPECIFIC, but also those upon which the greater part 

 of the GENERA of this group have been founded, and even 

 in some instances those of its ORDERS " (Foraminifera, 

 Preface, x). Yet this same group had been divided 

 by D'Orbigny and other authors into a number of 

 clearly defined families, genera, and species, which these 

 careful and conscientious researches have shown to 

 have been almost all founded on incomplete knowledge. 

 Professor DeCandolle has recently given the results 

 of an extensive review of the species of Cupuliferas. 

 He finds that the best-known species of oaks are those 

 which produce most varieties and subvarieties ; that 

 they are often surrounded by provisional species ; 

 and, with the fullest materials at his command, two- 

 thirds of the species he considers more or less doubt- 

 ful. His general conclusion is, that (i in botany the 

 lowest series of groups, SUBVARIETIES, VARIETIES, and 

 RACES are very badly limited; these can be grouped into 

 SPECIES a little less vaguely limited, which again can 

 be formed into sufficiently precise GENERA.." This 



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