THE BEGINNINGS OF LIFE. 137 



lowing broad views concerning the succession of Life 

 on the earth l : 



c We know, in fact, that in the strata of older date 

 than, or of the same epoch as, the coal formations, there 

 are no remains of any terrestrial animal, whilst at this 

 epoch vegetation had already made great progress, and 

 was composed of plants as remarkable for their forms 

 as for their gigantic stature. At a later period ter- 

 restrial vegetation loses in a great measure the signal 

 vigour which it formerly possessed, and cold-blooded 

 vertebrate animals become extremely numerous: this 

 is what is observed during the third period. 



c Subsequently, plants become more varied, more per- 

 fect ; but the analogues of those that existed originally 

 are reduced to a vastly smaller stature: this is the 

 epoch of the appearance of the most perfect animals, 

 of animals breathing air, of mammalia, and birds. 



c ls there no means of discovering some cause adequate 

 to explain in a natural way this vast development, this 

 vigorous growth of plants breathing air, even from the 

 most remote epochs in the formation of the globe? 

 And, on the other hand, of the appearance of warm- 

 blooded animals, that is to say, of animals whose aerial 

 respiration is most active in the last periods of its 

 formation only ? May not this difference in the epoch 

 of the appearance of these two classes of beings depend 

 on the difference in their mode of respiration, and 



1 Quoted in Dumas and Boussingault's ' Chemical and Physiological 

 Balance of Organic Nature.' 



