Lefevre — The Advance of Zoology in the Nineteenth Century. 87 



certain ends ; but he believed that the succession of forms in 

 *evolution was due to the action of an internal perfecting prin- 

 ciple originally implanted by the Divine Intelligence. During 

 the sixteenth and seventeenth centuries more or less direct 

 contributions were made to the foundations of modern evolu- 

 tion by the philosophers Bacon, Descartes, Leibnitz, Kant 

 and others. But it is to the great naturalists or nature-phi- 

 losophers of the latter half of the eighteenth century and the 

 first half of the nineteenth that we must look for the definite 

 formulation of evolutionary theories, to Buff on, Erasmus 

 Darwin, Lamarck, Goethe, Treviranus and Geoffroy St. Hilaire. 

 Although each of these naturalists, especially Goethe, clearly 

 recognized the evolutionary principle as opposed to the doctrine 

 of special creation, Lamarck alone proposed a definite system 

 by setting forth certain factors to account for adaptations and 

 the origin of species, and it is to his theory that we must 

 confine our attention in this place in speaking of pre-Darwinian 

 evolutionists. The complete expression of his theory appeared 

 in his ** Philosophic Zoologique " in 1809. 



Lamarck taught that first organisms of the simplest struc- 

 ture arose through spontaneous generation, and that from these 

 there have been developed in the course of a vast period of 

 time, through gradual change, all of the present species of 

 animals and plants without any break in the continuity. The 

 last and highest member of the series is man who has there- 

 fore had a common origin with the lower forms. The causes 

 which have brought about these changes, or in other words the 

 factors of evolution, according to Lamarck, are the inherited 

 effects of use and disuse, the action of the environment, and the 

 influence of conscious effort or willing on the part of the 

 animal. The giraffe for example, has acquired a long neck 

 because he has been compelled to stretch his neck in order 

 to browse upon the leaves of trees, living as he does in regions 

 of sparse vegetation; and again, the blind fish living in dark 

 caves has lost its eye- sight through disuse of its organs of 

 vision. Lamarck regarded the influence of environment as 

 of secondary importance and as acting only indirectly upon 

 animals by changing the conditions for the use of organs. 



In maintaining a continuity of development for all organic 



