Chap. VI., ON HBTEEOSTYLED PLANTS. 277 



of the three female ants, illegitimately fertilised by a 

 male of a different size, would resemble in a whole 

 series of relations the hybrid offspring from a cross 

 between two distinct species of ants. They would be 

 dwarfed in nature, and more or less, or even utterly 

 barren. Naturalists are so much accustomed to behold 

 great diversities of structure associated with the two 

 sexes, that they feel no surprise at almost any amount 

 of difference ; but differences in sexual nature have been 

 thought to be the very touchstone of specific distinction. 

 We now see that such sexual differences — the greater or 

 less power of fertilising and being fertilised — may char- 

 acterise the co-existing individuals of the same species, 

 in the same manner as they characterise and have kept 

 separate those groups of individuals produced during 

 the lapse of ages, which we rank and denominate as 

 distinct species. 



