CHAP. II. RESEMBLE VARIETIES. 57 



should be ranked as species or varieties. Now Fries 

 has remarked in regard to plants, and Westwood in 

 regard to insects, that in large genera the amount of 

 difference between the species is often exceedingly small. 

 I have endeavoured to test this numerically by averages, 

 and, as far as my imperfect results go, they always con- 

 firm the view. I have also consulted some sagacious 

 and most experienced observers, and, after deliberation, 

 they concur in this view. In this respect, therefore, the 

 species of the larger genera resemble varieties, more 

 than do the species of the smaller genera. Or the case 

 may be put in another way, and it may be said, that 

 in the larger genera, in which a number of varieties or 

 incipient species greater than the average are now 

 manufacturing, many of the species already manufac- 

 tured still to a certain extent resemble varieties, for 

 they differ from each other by a less than usual amount 

 of difference. 



Moreover, the species of the large genera are related 

 to each other, in the same manner as the varieties of 

 any one species are related to each other. No natu- 

 ralist pretends that all the species of a genus are equally 

 distinct from each otl\er ; they may generally be divided 

 into sub-genera, or sections, or lesser groups. As Fries 

 has well remarked, little groups of species are generally 

 clustered like satellites around certain other species. And 

 what are varieties but groups of forms, unequally related 

 to each other, and clustered round certain forms — that is, 

 round their parent-species ? Undoubtedly there is one 

 most important point of difference between varieties and 

 species ; namely, that the amount of difference between 

 varieties, when compared with each other or with their 

 parent-species, is much less than that between the spe- 

 cies of the same genus. But when we come to discuss 

 the principle, as I call it, of Divergence of Character, 



d3 



