SUMMARY OF* PHILOSOPHIE ZOOLOGIQUE: 277 



fossil forms is due to the fact that our living species 

 are modified descendants of the fossil ones. Such large 

 parts of the globe were still practically unknown in 

 Lamarck's time, and the recent discovery of the orni- 

 thorhynchus has raised such hopes as to what might 

 yet be found in Australia, that he was inclined to think 

 that only such creatures as man found hurtful to him, 

 as, for example, the megatherium and the mastodon, 

 had become truly extinct, nor was he, it would seem, 

 without a hope that these would yet one day be dis- 

 covered. The climatic and geological changes that 

 have occurred in past ages, would, he believed, account 

 for all the difference which we observe between living 

 and fossil forms, inasmuch as they would have changed 

 the conditions under which animals lived, and therefore 

 their habits and organs would have become correspond- 

 ingly modified. He therefore rather wondered to find 

 so much, than so little, resemblance between existing 

 and fossil forms. 



Buffon took a juster view of this matter ; it will be 

 remembered that he concluded his remarks upon the 

 mammoth by saying that many species had doubtless 

 disappeared without leaving any living descendants, 

 while others had left descendants which had become 

 modified. 



Lamarck anticipated Lyell in supposing geological 

 changes to have been due almost entirely to the con- 

 tinued operation of the causes which we observe daily 

 at work in nature : thus he writes : 



" Every observer knows that the surface of the earth 

 has changed; every valley has been exalted, the 



