I shall have to return to this subject in the chapter on classification, but I may add that as, according to this view, extremely few of the more ancient species have transmitted descendants to the present day, and, as all the descendants of the same species form a class, we can understand how it is that there exist so few classes in each main division of the animal and vegetable kingdoms.
Sailkapenari buruzko kapituluan etorri beharko dut berriro kontu honetara, baina gehi nezake hemen, ikuspegi honen arabera, antzinako espezieetarik oso-oso gutxik eman duela ondorengorik gaur arte, eta, espezie bereko ondorengo guztiek klase bat osatzen dutenez gero, uler dezakegu zergatik hain klase gutxi dagoen animali eta landare-erreinuko dibisio nagusi bakoitzean.