if we compare, for instance, the number of endemic land-shells in madeira, or of endemic birds in the galapagos archipelago, with the number found on any continent, and then compare the area of the island with that of the continent, we shall see that this is true.

This is all lower case. Can you fix that?
If we compare, for instance, the number of endemic land-shells in Madeira, or of endemic birds in the Galapagos Archipelago, with the number found on any continent, and then compare the area of the island with that of the continent, we shall see that this is true.