50 SPECIES OF LARGER GENERA VARIABLE. 



large trees grow, we expect to find saplings. Where many 

 Species of a genus have been formed through variation, 

 circumstances have been favorable for variation ; and hence 

 We might expect that the circumstances would generally still 

 be favorable to variation. On the other hand, if we look at 

 each species as a special act of creation, there is no apparent 

 reason why more varieties should occur in a group having 

 many species, ihan in one having few. 



To test the truth of this anticipation I have arranged thf 

 plants of twelve countries, and the coleopterous insects oi 

 two districts, into two nearly equal masses, the species of 

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

 genera on the other side, and it has invariably proved to be 

 the case that a larger proportion of the species on the side 

 of the larger genera presented varieties, than on the side of 

 the smaller genera. Moreover, the species of the large 

 genera which present any varieties, invariably present a 

 larger average number of varieties than do the species of 

 the small genera. Both these results follow when another 

 division 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, that where many species of a genus 

 have been formed, on an average many are still forming* 

 and this certainly holds good. 



