The following extract from his very instructive book on Lake Superior explains this view: "There are in animals peculiar adaptations which are characteristic of their species, and which cannot be supposed to have arisen from subordinate influences.

Those which live in shoals cannot be supposed to have been created in single pairs.

Those which are made to be the food of others cannot have been created in the same proportions as those which live upon them.

Those which are everywhere found in innumerable specimens must have been introduced in numbers capable of maintaining their normal proportions to those which live isolated and are comparatively and constantly fewer.

For we know that this harmony in the numerical proportions between animals is one of the great laws of nature.