7(5 ESSAY ON CLASSIFICATION. 



are placed, have no more influence upon their essential 

 characters than the lapse of time. 



The facts bearing upon these two subjects are too well 

 known to require special illustration. I will, therefore, 

 allude only to a few points, to avoid even the possibility 

 of a misapprehension of my statements. That animals of 

 different geological periods differ specially, en masse, from 

 those of preceding or following formations, is a fact satis- 

 factorily ascertained. Between two successive geological 

 periods, then, changes have taken place among animals 

 and plants. But none of those primordial forms of life 

 which naturalists call species are known to have changed 

 during any of these periods. It cannot be denied, that 

 the species of different successive periods are supposed 

 by some naturalists to derive their distinguishing features 

 from changes which have taken place in those of pre- 

 ceding ages ; but this is a mere supposition, supported 

 neither by physiological nor by geological evidence ; and 

 the assumption, that animals and plants change in a 

 similar manner during one and the same period, is equally 

 gratuitous. On the contrary, it is known, by the evidence 

 furnished by the Egyptian monuments, and by the most 

 careful comparison between animals found in the tombs 

 of Egypt with living specimens of the same species ob- 

 tained in the same country, that there is not the shadow 

 of a difference between them for a period of about five 

 thousand years. These comparisons, first instituted by 

 Cuvier, have proved, that, as far as it has been possible to 

 carry back the investigation, it does not afford the begin- 

 ning of an evidence that species change in the course of 

 time, if the comparisons be limited to the same great cos- 

 mic epoch. Geology only shows that at different periods 1 



1 I trust no reader will be so igno- to infer from the use of the word 

 rant of the facts here alluded to as " period" for different eras and epochs 



