278 Professor Pictet on the Succession of Animals. 



to explain slight modifications of a type, but rather transi- 

 tions between forms widely separated from each other. Some 

 naturalists have not drawn back before any of these transi- 

 tions, and they have admitted, that the reptiles of the se- 

 condary epoch had their parents in the fishes of the primary 

 epoch, and their descendants in the mammifera of the ter- 

 tiary period. Where is the physiologist that will admit such 

 conclusions as these \ And yet we must go that length be- 

 fore we can derive all the geological faunas from the firsts 

 by the simple transition of species into each other, and with- 

 out the direct intervention of a creative power, operating at 

 the origin of each of the geological epochs. 



And even, if, in order to produce such results, it were sup- 

 posed, contrary to what we have done, that very great changes 

 have taken place in temperature, and the media in which ani- 

 mals lived, or a younger nature, all the laws of physiology 

 would not be less violated. These extreme differences in 

 exterior agents may well be considered as fitted to destroy 

 species, and this would probably be their natural result, but 

 not to modify them in their essential forms. 



It, therefore, appears to me evident, that it is impossible to 

 admit, as an explanation, the passing of species into one an- 

 other. The possible limits of these transitions, even suppos- 

 ing, as I shall afterwards state, that the immense duration of 

 time might have rendered them somewhat more probable 

 than the study of the existing phenomena will allow, fall in- 

 finitely short of the diff*erences which distinguish two succes- 

 sive faunas. Above all, we cannot by this means compre- 

 hend the appearance of types altogether new, for which we 

 must necessarily, in the present state of the science, have re- 

 course to the idea of creations posterior to the first. 



The theory of successive creations, therefore, alone remains 

 possible ; and, in truth, it is far from being free from rather 

 weighty objections, although I am of opinion, that, in the 

 present state of our knowledge, it is the only one admissible. 



I must, however, here repeat, that this theory is not com- 

 pletely satisfactory ; it does not appear to me to explain suf- 

 ficiently all the facts, and I cannot help believing, that it is 

 destined to act merely a provisionary part. It explains very 



