70 SPECIES OP LARGER GENERA VARIABLE. [Chap. IL 



the species of the larger genera on one side, and those 

 of the smaller genera on the other side, and it has in- 

 variably proved to be the case that a larger propor- 

 tion of the species on the side of the larger genera pre- 

 sented varieties, than on the side of the smaller genera. 

 Moreover, the species of the large genera which pre- 

 sent any varieties, invariably present a larger average 

 number of varieties than do the species of the small 

 genera. Both these results follow when another divis- 

 ion is made, and when all the least genera, with from 

 only one to four species, are altogether excluded from 

 the tables. These facts are of plain signification on 

 the view that species are only strongly-marked and 

 permanent varieties; for wherever many species of the 

 same genus have been formed, or where, if we may use 

 the expression, the manufactory of species has been 

 active, we ought generally to find the manufactory still 

 in action, more especially as we have every reason to 

 believe the process of manufacturing new species to be 

 a slow one. And this certainly holds true, if varieties 

 be looked at as incipient species; for my tables clearly 

 show as a general rule that, wherever many species of a 

 genus have been formed, the species of that genus 

 present a number of varieties, that is of incipient 

 species, beyond the average. It is not that all large 

 genera are now varying much, and are thus increasing 

 in the number of their species, or that no small genera 

 are now varying and increasing; for if this had been 

 so, it would have been fatal to my theory; inasmuch 

 as geology plainly tells us that small genera have in 

 the lapse of time often increased greatly in size; and 

 that large genera have often come to their maxima, 

 decline, and disappeared. All that we want to show is, 



