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.

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.

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 great age of the earth will appear greater to man when he understands the origin of living organisms and the reasons for the gradual development and improvement of their organization. This antiquity will appear even greater when he realizes the length of time and the particular conditions which were necessary to bring all the living species into existence. This is particularly true since man is the latest result and present climax of this development, the ultimate limit of which, if it is ever reached, cannot be known.

Habits form a second nature.

All known living bodies are sharply divided into two special kingdoms, based upon the essential differences which distinguish animals from plants, and in spite of what has been said, I am convinced that these two kingdoms do not really merge into one another at any point.