A race of animals or of plants marked by any peculiar character which has always been constant and undeviating constitutes a species; and two races are considered as specifically different, if they are distinguished from each other by some characteristic which one cannot be supposed to have acquired, or the other to have lost through any known operation of physical causes; for we are hence led to conclude that the tribes thus distinguished have not descended from the same original stock." (14/10.

Prichard, ed.

1836-7, Volume I., page 106.

This passage is almost identical with that quoted from the second edition, Volume I., page 90.

The latter part, from "and two races...," occurs in the second edition, though not quoted above.) As was his custom, Mr.Darwin pinned at the end of the first volume of the 1841-51 edition a piece of paper containing a list of the pages where marked passages occur.