40 U. UNCERTAINTY OF SPECIES. 



changes in the genus, under which any given species was 

 placed, being allowed for in reckoning the number of 

 sjiecies. The corresponding allowance, towards reduc- 

 tion of numerical discrepancies, could not be so satisfac- 

 torily made in the case of added species ; because it is 

 occasionally too difficult to decide whether an Author 

 was unacquainted with the " species," since described as 

 novelties by his successors, or whether he had regarded 

 them simplj^ as unimportant varieties of those which were 

 described by himself. Such editions of the works as 

 happen to be at hand ai-e here used, and are identified by 

 their dates. 



Varying number of Species. 



Thus, whether we compare together different Authors, 

 publishing at nearly the same dates, or the same Author, 

 publishing at different dates, it is seen that much discre- 

 pancy existed in their ideas of species. But a further 

 contrast between the varying views of the same Author, 

 at short intervals, may even more clearly show how 

 uncertain still are the practical ideas about species, as 



