SUMMARY OF ' PHILOSOPHIE ZOOLOGIQUE? 263 



where organic beings had already attained a con- 

 siderable development. Nature has done all by slow 

 gradations, both organs and faculties being the out- 

 come of a progressive development.* 



" The mere composition of an animal is but a small 

 part of what deserves study in connection with the 

 animal itself. The effects of its surroundings in causing 

 new wants, the effects of its wants in giving rise to 

 actions, those of its actions in developing habits and 

 tendencies, the effects of use and disuse as affecting any 

 organ, the means which nature takes to preserve and 

 make perfect what has been already acquired these 

 are all matters of the highest importance, f 



" In their bearing upon these questions the inverte- 

 brate animals are more important and interesting than 

 the vertebrate, for they are more in number, and being 

 more in number are more varied ; their variations are 

 more marked, and the steps by which they have 

 advanced in complexity are more easily observed.^ 



" I propose, therefore, to divide this work into three 

 parts, of which the first shall deal with the conventions 

 necessary for the treatment of the subject, the im- 

 portance of analogical structures, and the meaning 

 which should be attached to the word species. I will 

 point out on the one hand the evidence of a graduated 

 descending scale, as existing between the highest and 

 the lowest organisms ; and, on the other, the effect of 

 surroundings and habits on the organs of living beings, 

 as the cause of their development or arrest of deve- 

 lopment. Lastly, I will treat of the natural order of 



* 'Phil. Zool.,' torn. i. pp. 26, 27. t Page 28. J Pages 28-31 



