independently of several relations which we cannot disregard, I
should place the head of a tortoise on the neck of certain birds, I
should perceive almost no disparity in the general physiognomy of
the factitious animal; and on the other side, the saurians,
especially the 'planicaudes,' such as the crocodiles, seem to have
given origin to the amphibious mammals.

"If the branch of the Chelonians has given rise to birds, we can yet
presume that the palmipede aquatic birds, especially the
_brevipennes_, such as the penguins and the _manchots_, have given
origin to the monotremes.

"Finally, if the branch of saurians has given rise to the amphibious
mammals, it will be most probable that this branch is the source
whence all the mammals have taken their origin.

"I therefore believe myself authorized to think that the terrestrial
mammals originally descended from those aquatic mammals that we call
Amphibia. Because the latter being divided into three branches by
the diversity of the habits which, with the lapse of time, they have
adopted, some have caused the formation of the Cetacea, others that
of the ungulated mammals, and still others that of the unguiculate
mammals.

"For example, those of the Amphibia which have preserved the habit
of frequenting the shores differ in the manner of taking their food.
Some among them accustoming themselves to browse on herbage, such as
the morses and lamatines, gradually gave origin to the ungulate
mammals, such as the pachyderms, ruminants, etc.; the others, such
as the Phocidae, contracting the habit of feeding on fishes and
marine animals, caused the existence of the unguiculate mammals, by
means of races which, while becoming differentiated, became entirely
terrestrial.

"But those aquatic mammals which would form the habit of never
leaving the water, and only rising to breathe at the surface, would
probably give origin to the different known cetaceans. Moreover, the
ancient and complete habitation of the Cetacea in the ocean has so
modified their structure that it is now very difficult to recognize
the source whence they have derived their origin.

"Indeed, since the enormous length of time during which these
animals have lived in the depths of the sea, never using their hind
feet in seizing objects, their disused feet have wholly disappeared,
as also their skeleton, and even the pelvis serving as th