xxviii INTRODUCTION 



after that comes the respiratory system ; and third, the 

 circulatory system. This order of importance is arrived at 

 in the following way. Starting from the higher extremity 

 of the animal series, where man is placed, he descends the 

 series of gradually simplifying animals. One after another, 

 he finds the different systems of organs dying out : and the 

 importance of each system is judged by the distance he has 

 to travel down the series before that system becomes extinct. 

 Thus the circulatory system extends throughout Lamarck's 

 eight highest classes, viz. : — mammals, birds, reptiles, fishes, 

 molluscs, cirrhipedes, annelids and crustaceans, and there 

 ends. The respiratory and nervous systems extend through 

 these and also the two succeeding classes of arachnids and 

 insects. They are therefore held to be more essential than 

 the circulatory system. Of these two again, the nervous 

 system is the more essential, since " it has produced the most 

 exalted of animal faculties, and is necessary to muscular 

 activity." I confess it is not obvious why the alimentary 

 system does not take precedence of all others, for it is 

 described as extending through the three further classes 

 of worms, radiarians and polyps, only ending at the in- 

 fusorians. Since Lamarck (as I shall shortly explain) 

 believed in an evolution from the simplest to the most com- 

 plex animals, he naturally assumed that the earliest system 

 of organs to be developed in the course of that evolution 

 must be the system most essential to life in the higher animals. 

 The least essential of the features to be considered in the 

 determination of affinities are, in his opinion, the external 

 characters of animals : differences of external characters 

 are therefore to be used only for the determination of species. 

 For more fundamental distinctions, more essential characters 

 are to be considered. 



Lamarck found the " productions of nature " commonly 

 divided into the three kingdoms of animal, vegetable and 

 mineral. He proposed the abolition of this scheme, and the 

 substitution of another in which all bodies were to be divided 

 into organic and inorganic. For the science which deals 



