ii.] DEVELOPMENT OF ANIMAL LIFE 131 



fusing to manufacture organic out of inorganic material 

 and taking organic substances ready made from organ- 

 isms that had turned toward the vegetative life, so, among 

 the animal species themselves, many contrived to live 

 at the expense of other animals. For an organism that is 

 animal, that is to say mobile, can avail itself of its mobility 

 to go in search of defenseless animals, and feed on them 

 quite as well as on vegetables. So, the more species be- 

 came mobile, the more they became voracious and danger- 

 ous to one another. Hence a sudden arrest of the entire 

 animal world in its progress towards higher and higher 

 mobility; for the hard and calcareous skin of the echino- 

 derm, the shell of the mollusc, the carapace of the crustacean 

 and the ganoid breast-plate of the ancient fishes probably 

 all originated in a common effort of the animal species 

 to protect themselves against hostile species. But this 

 breast-plate, behind which the animal took shelter, 

 constrained it in its movements and sometimes fixed 

 it in one place. If the vegetable renounced consciousness 

 in wrapping itself in a cellulose membrane, the animal 

 that shut itself up in a citadel or in armor condemned 

 itself to a partial slumber. In this torpor the echinoderms 

 and even the molluscs live to-day. Probably arthropods 

 and vertebrates were threatened with it too. They escaped, 

 however, and to this fortunate circumstance is due the 

 expansion of the highest forms of life. 



In two directions, in fact, we see the impulse of life 

 to movement getting the upper hand again. The fishes 

 exchanged their ganoid breast-plate for scales. Long 

 before that, the insects had appeared, also disencumbered 

 of the breast-plate that had protected their ancestors. 

 Both supplemented the insufficiency of their protective 

 covering by an agility that enabled them to escape their 

 enemies, and also to assume the offensive, to choose the 



