288 EVOLUTION, OLD AND NEW. 



called specific characters ; and as these specific cha- 

 racters have varied and come to differ since the period 

 when the species branched off from a common pro- 

 genitor, it is probable that they should still often be in 

 some degree variable, or at least more variable than 

 those parts of the organization which have for a very 

 long time remained constant." * 



The fact, then, that it is specific characters which 

 vary most is agreed upon by both Lamarck and Mr. 

 Darwin. Lamarck, however, maintains that it is these 

 specific characters which are most capable of being 

 affected by the habits of the creature, and that it is for 

 this reason they will be most variable, while Mr. Dar- 

 win simply says they are most variable, and that, 

 this being so, the favourable variations will be pre- 

 served and accumulated an assertion which Lamarck 

 would certainly not demur to. 



"Irregular degrees of perfection," says Lamarck, 

 " and degradation in the less essential organs, are due to 

 the fact that these are more liable than the more essential 

 ones to the influence of external circumstances: these 

 induce corresponding differences in the more outward 

 parts of the animal, and give rise to such considerable 

 and singular difference in species, that instead of being 

 able to arrange them in a direct line of descent, as we 

 can arrange the main groups, these species often form 

 lateral ramifications round about the main groups to 

 which they belong, and in their extreme development 

 are truly isolated." \ 



In his summary of the second chapter of his ' Origin 



* 'Origin of Species,' pp. 122, 123. t ' Phil. Zool.,' torn. i. p. 123. 



