1921] The Age of Insects 31 



ence of half-sleep. It is in this torpor that the echinoderms and even 

 the mollusks are living today. The arthropods and vertebrates 

 escaped from it and on this happy circumstance depends the present 

 development of the highest forms of life. 



"In two directions, indeed, do we see the impulse of active life re- 

 gaining the upper hand. The fishes exchange their ganoid armor for 

 scales. Long before them the insects had made their appearance, 

 having also rid themselves (of most) of the armor that once protected 

 their ancestors. In both groups the inefficiency of the protective en- 

 velope was compensated for by a nimbleness that enabled them to 

 escape their enemies and also to take the offensive and to select the 

 place and time of the encounter." 



These remarks rest on a solid foundation but they should be mod- 

 ified in one particular which is of paramount importance in the ex- 

 planation of the structure and the special psychology of the arthro- 

 pods. These animals have never lost the chitinous armor that pro- 

 tected their primitive ancestors. They have preserved it in its en- 

 tirety and with greater or less thickness. Coleoptera, crabs, scor- 

 pions, and thousand-legs of our times are by no means inferior in this 

 regard to the ancient forms from which they are descended. 



As a matter of fact they are covered today, as in times of yore, 

 with an external skeleton of chitin. That is why Edmund Perrier, in 

 his desire to emphasize their dominant character, has called them 

 Chitinophores. To escape imprisonment within their protective en- 

 velope, to acquire the flexibility and mobility necessary to their evolu- 

 tion, they underwent certain superficial modifications. These con- 

 sisted in the division of the armor into several pieces by means of artic- 

 ular lines, along which the chitin is less thick than elsewhere, thus 

 allowing the pieces to move one upon the other. This is the very waj^ 

 in which they became arthropods, at once acquiring agility without 

 losing their protective cover. Naturally such joints were formed 

 wherever the several segments, arranged in a row and constituting the 

 body of the animal, came together. As a result, these segments ac- 

 quire a certain independence and their uniformity is to a certain ex- 

 tent preserved. Indeed, we see that many arthropods possess a pair 

 of appendages on each segment (Myriapods and the majority of Crus- 

 taceans) and that the insects most remote in this regard from the 

 primitive types are still provided with seven pairs of appendages (one 

 pair of antennae, three pairs of buccal appendages and three pairs of 

 legs) not to speak of the modified or rudimentary organs to be seen on 



