ARISTOTLE ON THE ORIGIN OF LIFE. ai 
there alone, during a period of more than two thousand 
years, in the region of empirico-philosophical knowledge of 
nature, and especially in his knowledge of organic nature, is 
proved to us by the precious remains of his but partially 
surviving works. In them many traces are found of a 
theory of natural development. Aristotle assumes, as a 
matter of certainty, that spontaneous generation was the 
natural manner in which the lower organic creatures came 
into existence. He describes animals and plants originating 
- from matter itself, through its own original force; as, for 
example, moths from wool, fleas from putrid dung, wood-lice 
from damp wood, etc. But as the distinction of organic 
species, which Linnzeus only arrived at two thousand years 
later, was unknown to him, he could form no ideas about 
their genealogical relations. 
The fundamental notion of the theory of development, 
that the different species of animals and plants have been 
developed from a common primary species by transformation, 
could of course only be clearly asserted after the kinds or 
species themselves had become better known, and after the 
extinct species had been carefully examined and compared 
with the living ones. This was not done until the end 
of the last and the beginning of the present century. 
It was not until the year 1801 that the great Lamarck 
expressed the theory of development, which he, in 1809, 
further elaborated in his classical “ Philosophie Zoologique.” 
While Lamarck and his countryman, Geoffroy St. Hilaire, in 
France, opposed Cuvier’s views, and maintained a natural 
development of organic species by transformation and 
descent, Goethe and Oken at the same time pursued the 
same course in Germany, and helped to establish the theory 
