186 THE TRANSFORMATIONS OF THE ANIMAL WORLD 



sheaf, B, B 1 , B 2 . . ., by characteristics more im- 

 portant than those which distinguish the forms of 

 the same group. Some give to these groupings of 

 species the name of sub-genus, while others in- 

 dividualize them more completely by according 

 them the hierarchical value of a true genus. But, 

 this question of words apart, we may affirm that 

 these small limited genera constitute the most 

 solid and the most natural grouping in all zoo- 

 logical nomenclature. It goes without saying that 

 the sub-genera, or sections, as they are sometimes 

 termed, may be united, if desired, into genera more 

 important and wider in extent. But, in all cases 

 and this is the essential point these various group- 

 ings, species, sub-genera, great genera, preserve 

 towards each other a complete independence, and 

 their limits, except in very rare cases, can be settled 

 satisfactorily. 



It would be the same if, in lieu of considering 

 the living fauna, we directed our analysis towards 

 one or other of the faunas which lived in early 

 times, provided we deal with animals rigorously 

 contemporaneous, that is to say, belonging to the 

 same strictly limited geological horizon. There 

 we should again meet with morphological variation, 

 either individual or regional, under the well-known 

 form of varieties or local races ; but we should, in 

 general, have no difficulties in demarcating the 

 large species, the sub-genera, and, above all, the 

 great natural genera. 



But the problem presents itself in very different 

 conditions if, instead of considering the elements of 

 contemporaneous faunas, we attempt to apply the 



