2QO EVOLUTION, OLD AND NEW. 



Larnarck now rapidly reviews previous classifications, 

 and propounds his own, which stands thus : I. Verte- 

 brata, consisting of Mammals, Birds, Fishes, and 

 Reptiles. II. Invertebrata, consisting of Molluscs, 

 Centipedes, Annelids, Crustacea, Arachnids, Insects, 

 Worms, Radiata, Polyps, Infusoria. 



" The degradation of organism," he concludes, " in 

 this descending scale is not perfectly even, and cannot 

 be made so by any classification, nevertheless there is 

 such evidence of sustained degradation in the principal 

 groups as must point in the direction of some under- 

 lying general principle." * 



Lamarck's sixth chapter is headed " Degradation and 

 Simplification of the Animal Chain as we proceed 

 downwards from the most complex to the most simple 

 Organisms." 



" This is a positive fact, and results from the opera- 

 tion of a constant law of nature ; but a disturbing cause, 

 which can be easily recognized, varies the regular 

 operation of the law from one end to the other of the 

 chain of life, f 



"We can see, nevertheless, that special organs 

 become more and more simple the lower we descend ; 

 that they become changed, impoverished, and attenu- 

 ated little by little ; that they lose their local centres, 

 and finally become definitely annihilated before we reach 

 the lowest extremity of the chain. } 



" As has been said already, the degradation of 

 organism is not always regular ; such and such an 

 organ often fails or changes suddenly, and sometimes 



* 'Phil. Zool.,' torn. i. p. 140. f Page 142. J Page 143. 



