THE TRIGGER-FISH 



there. Their presence and multiplicity are typical of 

 the period. The Palaeozoic era belonged to them, as 

 the Mesozoic era belonged to the reptiles, and as the 

 Tertiary of today belongs to the mammals and birds. 

 Except for the sharks, they have disappeared and the 

 sceptre of the power of life has passed to others. 



This first change, this transfer of power, took place 

 during the Mesozoic era. We can follow the phases 

 of its transformation in fossils and in the succession of 

 deposits in which it is recorded. First the older 

 type of armoured fish grows smaller in numbers: 

 then we find, appearing and multiplying, fishes with 

 a bony skeleton of the new type, more agile, more 

 flexible, and more varied. At the same time, by a 

 remarkable coincidence, life on land changed in an 

 exactly similar manner. Flowering plants took the 

 place of the heavy vegetation of flowerless plants 

 and cone-bearing trees. Then came the insect that 

 develops from a grub, including the many-hued host 

 of butterflies. The huge reptiles were replaced by 

 the smaller birds, created, as Buffon wrote, " by 

 Nature in a moment of gaiety ". Life on earth and 

 life in the waters changed at one and the same time. 



In this transformation, Nature became more gracious, 

 showed herself more gentle to the creatures she had 

 brought into being. She began with clumsy structures 

 in which matter predominated ; she ended by producing 

 organisms in which the activities of life can be mani- 

 fested with the employment of less material substance. 

 On the long road of Time, which the living world has 

 travelled since its remote beginning, difficulties grow 

 less, and hardships diminish. As life makes progress, 

 it grows easier. This, in fact, is the mark of its progress. 



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