94 Hypothesis of Structure of Germ Substance 



easily able to assume any new somatic character what- 

 ever which may be imposed upon them. It makes no 

 difference in the case of the still unspecialized cell, or 

 even in that of the cell which is in the first stages of 

 specialization, whether the somatizing stimulus is onto- 

 genetic, proceeding by indirect ways from the central 

 zone, or functional, induced by the environment. For 

 the embryonic cell is in itself thoroughly plastic. Con- 

 sequently the young soma would also be plastic if 

 it were not continually influenced by the formative stimuli 

 proceeding from the central zone of development. This 

 influence though it is more feeble than the functional stim- 

 ulus proceeding from the environment and consequently 

 unable to resist it, has nevertheless the advantage of be- 

 ing continuously in action, and so of gaining the ground 

 lost, as soon as the action of the environment ceases. 



The cells of the adult soma are on the contrary less 

 plastic, because they are already considerably specialized. 

 But every modification which their limited plasticity per- 

 mits in them remains, since the opposition of the central 

 zone of development has already ceased. The adult 

 organism is much less elastic. But in respect to the 

 permanence of results it is more plastic than the young 

 one. 



And, as already said, this is entirely confirmed not 

 only by the most commonplace phenomena, but also by 

 the most careful embryologic researches. In fact con- 

 siderable changes of form, which would be destructive 

 to an adult organism are, on the contrary, very well 

 borne by the young. But attentive observation of these 

 processes shows us also, as stated, that the younger the 

 organism the greater is its elasticity, which tends, when 

 the disturbing action has ceased, to restore it to its 



