342 LAMARCK, HIS LIFE AND WORK 
that of amphibious mammals, which have given in 
their turn origin to all the other mammals.* 
“ Indeed, the fishes having caused the formation 
of Batrachia, and these of the Ophidian reptiles, both 
having only one auricle in the heart, nature has 
easily come to give a heart with a double auricle to 
other reptiles which constitute two special branches ; 
finally, she has easily arrived at the end of forming, 
in the animals which had originated from each of 
these branches, a heart with two ventricles. 
“ Thus, among the reptiles whose heart has a double 
auricle, on the one side, the Chelonians seem to have 
given origin to the birds; if, independently of several 
rclations 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. 
“Tf the branch of the Chelonians has given rise to 
birds, we can yet presume that the palmipede aquatic 
birds, especially the drevipennes, such as the penguins 
and the manchots, have given origin to the mono- 
LreEmes: 
“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 mam- 
mals have taken their origin. 
“T 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 forma- 
* This sagacious, though crude suggestion of the origin of birds 
and mammals from the reptiles is now, after the lapse of nearly a 
century, being confirmed by modern morphologists and paleontologists. 
