; and it is really surprising to note the endless points of structure and constitution in which the varieties and sub-varieties differ slightly from each other.

The whole organisation seems to have become plastic, and departs in a slight degree from that of the parental type.

Any variation which is not inherited is unimportant for us.

But the number and diversity of inheritable deviations of structure, both those of slight and those of considerable physiological importance, are endless.