GHAPTIER XViIl 
THE “ PHILOSOPHIE ZOOLOGIQUE ” 
LAMARCK’S mature views on the theory of descent 
comprise a portion of his celebrated Phzlosophie zoo- 
logique. We will let him tell the story of creation by 
natural causes so far as possible in his own words. 
In the avertissement, or preface, he says that his 
experience has led him to realize that a body of pre- 
cepts and of principles relating to the study of 
animals and even applicable to other parts of the 
natural sciences would now be useful, our knowledge 
of zodlogical facts having, for about thirty years, made 
considerable progress. 
After referring to the differences in structure and 
faculties characterizing animals of different groups, 
he proceeds to outline his theory, and begins by 
asking : 
“How, indeed, can I consider the singular modifi- 
cation in the structure of animals, as we glance over 
the series from the most perfect to the least perfect, 
without asking how we can account for a fact so 
positive and so remarkable—a fact attested to me by 
so many proofs? Should I not think that nature has 
successively produced the different living beings by 
proceeding from the most simple to the most com- 
pound; because in ascending the animal scale from 
the most imperfect up to the most perfect, the organi- 
