As we have seen in the last chapter that some forms have retained nearly the same character from an enormously remote geological period, so certain species have migrated over vast spaces, and have not become greatly or at all modified.
Nola forma batzuek antzina-antzinako aldi geologikoetatik hona ezaugarri ia berberei eutsi dioten, aurreko kapituluan ikusi dugun moduan, halaxe zenbait espezie ere arlo oso zabaletan zehar hedabanatu dira eta ezer gutxi edo bat ere ez dira aldatu.