However, if we consider that all the characteristics which have been cited are only differences in degree of structure, may we not suppose that this special condition of organization of man has been gradually acquired at the close of a long period of time, with the aid of circumstances which have proved favorable? What a subject for reflection for those who have the courage to enter into it!

All knowledge that is not the real product of observation, or of consequences deduced from observation, is entirely groundless and illusory.

The form follows the function.

Now this circumscribed power, which we have scarcely examined, scarcely studied, this power to whose actions we nearly always attribute an intention and a goal, this power, finally, that always does necessarily the same things in the same circumstances and nevertheless does so many and such admirable ones, is what we call 'nature' .

One must believe that every living thing whatsoever must change insensibly in its organization and in its form... One must therefore never expect to find among living species all those which are found in the fossil state, and yet one may not assume that any species has really been lost or rendered extinct.

The thesis that the living creatures have always been composed different species was established in a time where no sufficient observations had been made and when science hardly existed. This thesis is denied every day by those who have made accurate observations, who have long time observed nature and who have had the benefit from studying our musei's large and rich collections.

It is not always the magnitude of the differences observed between species that must determine specific distinctions, but the constant preservation of those differences in reproduction.