CiiAP. XII. AND PRESENT CHAPTER. 37I 



and space the lowly-orn^auized members of each class generally 

 change less than the highly-organized ; but there are in botli 

 cases marked exceptions to the rule. According to our theory 

 these several relations throughout time and space arc intelli- 

 gible ; for, whether we look to the forms of life which have 

 changed during successive ages, or to those which have changed 

 after having migrated into distant quarters, in both cases the 

 forms witliin each class arc connected by the same bond of or- 

 dinary generation ; and in both cases the laws of variation have 

 been the same, and modifications have been accumulated by 

 the same means of natural selection. 



