ii THE PLANT AND THE ANIMAL 115 



sheath bears witness to its relationship to the proto 

 plasm of animals, whilst in a large number of animal 

 species (generally parasites) phenomena of fixation, 

 analogous to those of vegetables, can be observed. 1 

 Here, again, it would be a mistake to claim that fixity 

 and mobility are the two characters which enable us 

 to decide, by simple inspection alone, whether we have 

 before us a plant or an animal. But fixity, in the 

 animal, generally seems like a torpor into which the 

 species has fallen, a refusal to evolve further in a 

 certain direction ; it is closely akin to parasitism and 

 is accompanied by features that recall those of vegetable 

 life. On the other hand, the movements of vegetables 

 have neither the frequency nor the variety of those of 

 animals. Generally, they involve only part of the 

 organism and scarcely ever extend to the whole. In 

 the exceptional cases in which a vague spontaneity 

 appears in vegetables, it is as if we beheld the accidental 

 awakening of an activity normally asleep. In short, 

 although both mobility and fixity exist in the vegetable 

 as in the animal world, the balance is clearly in 

 favour of fixity in the one case and of mobility in the 

 other. These two opposite tendencies are so plainly 

 directive of the two evolutions that the two kingdoms 

 might almost be defined by them. But fixity and 

 mobility, again, are only superficial signs of tendencies 

 that are still deeper. 



Between mobility and consciousness there is an 

 obvious relationship. No doubt, the consciousness 

 of the higher organisms seems bound up with certain 

 cerebral arrangements. The more the nervous system 

 develops, the more numerous and more precise become 



1 On fixation and parasitism in general, see the work of Houssay. 

 La Forme et la vie, Paris, 1900, pp. 721-807. 



