250 FROM THE GREEKS TO DARWIN 



see in the above tables, Lamarck's attempts at 

 reconstructing the tree of hfe were crude, but 

 considering the infancy of palaeontology and the 

 entire absence of embryological knowledge, his 

 speculations appear more to his credit. He sup- 

 posed that mammals passed through amphibious 

 mammals back to saurians similar to crocodiles. 

 The seals or aquatic mammalia gave rise to the 

 Unguiculates or clawed animals, and when the 

 claws became too long the Carnivores made ef- 

 forts to retract them. Some primitive mammals 

 did not leave the water at all but lost their limbs 

 and became the Cetacea. 



It is strange that Lamarck grasped the true 

 idea of extinction of the lower types, but not of 

 the higher types. He could not credit the extinc- 

 tion by any of the forces of Nature of such per- 

 fect forms as the Mastodon or the Palgeotherium 

 recently described by Cuvier, but he believed that 

 they had probably been exterminated by man or 

 that these species might still be found alive else- 

 where. He thoroughly believed in the extinction 

 of lower types — for example, of the Molluscs — 

 and that the lower types had given way to the 

 higher, the ranks of the lower types being con- 

 stantly replenished by incessant creation of the 

 lowest forms. 



As animals progressed, new forms were con- 

 stantly arising in the primitive scale. One of the 



v-s.. 



