276 Professor Pictet on the Succession of Animals. 



must have been in force from the beginning of creation, and 

 it is impossible to admit a real difference in their nature. 

 We can only conceive that each of them may have operated 

 within more extensive limits; thus, the temperature may have 

 been more elevated, the waters may have been charged with 

 more abundant substances, &c. ; but the influence of these 

 agents on organism must have been analogous to that which 

 similar circumstances would now exercise. The study of ani- 

 mals belonging to the ancient formations exhibits, moreover, an 

 organization very similar to that of existing beings ; and no- 

 thing authorises us to conclude, that they have been subjected 

 to a temperature very difi^erent from our own, or that they 

 have breathed an air of different composition. It seems to us, 

 therefore, that it would be to throw ourselves into a state of 

 uncertainty to admit modifications in the organism, produced 

 by changes of condition in the exterior agents ; and the ex- 

 pressions too frequently employed, yoi/^i^gr nature, more active 

 forces, &c., ought to be avoided, as representing false, exag- 

 gerated, or ill-defined ideas. 



If, then, we take up a more secure position, and infer what 

 is unknown from what is known, that is, if we apply to the 

 first ages of the globe the instruction which the study of re- 

 cent nature affords us, we will arrive at the following con- 

 clusions. 



All observations and researches of any value, now agree 

 in proclaiming the permanence of species. The thirty cen- 

 turies which have elapsed since the Egyptians embalmed the 

 carcases of men and animals, have had no influence what- 

 ever on the character of the animals found in Egypt ; the 

 crocodiles, ibises, and ichneumons, of the present day, are 

 identical with those which lived three thousand years ago on 

 the banks of the Nile. We cannot detect the slightest dif- 

 ference between existing individuals and those preserved as 

 mummies, not only in the essential organs, but even in the 

 most minute details of the number and form of the scales, 

 the dimensions of the bones, &c. This permanence of species 

 is, moreover, secured in nature by the important rules which 

 prevent their intermixture to form intermediate types. All 

 physiologists are aware, that if two species are not very 



