130 CREATIVE EVOLUTION [chap. 



separated soon from their common stock, the vegetable 

 falling asleep in immobility, the animal, on the con- 

 trary, becoming more and more awake and marching on 

 to the conquest of a nervous system. Probably the effort 

 of the animal kingdom resulted in creating organisms 

 still very simple, but endowed with a certain freedom 

 of action, and, above all, with a shape so undecided that 

 it could lend itself to any future determination. These 

 animals may have resembled some of our worms, but 

 with this difference, however, that the worms living to- 

 day, to which they could be compared, are but the empty 

 and fixed examples of infinitely plastic forms, pregnant 

 with an unlimited future, the common stock of the echino- 

 derms, molluscs, arthropods, and vertebrates. 



One danger lay in wait for them, one obstacle which 

 might have stopped the soaring course of animal life. 

 There is one peculiarity with which we cannot help 

 being struck when glancing over the fauna of primitive 

 times, namely, the imprisonment of the animal in a more 

 or less solid sheath, which must have obstructed and 

 often even paralyzed its movements. The molluscs 

 of that time had a shell more universally than those of 

 to-day. The arthropods in general were provided with a 

 carapace; most of them were crustaceans. The more 

 ancient fishes had a bony sheath of extreme hardness. 1 

 The explanation of this general fact should be sought, 

 we believe, in a tendency of soft organisms to defend 

 themselves against one another by making themselves, 

 as far as possible, undevourable. Each species, in the act 

 by which it comes into being, trends towards that which 

 is most expedient. Just as among primitive organisms 

 there were some that turned towards animal life by re- 



1 See, on these different points, the work of Gaudry, Essai de paUon- 

 tologie philosophique, Paris, 1896, pp. 14-16 and 78-79. 



