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24 THE EVOLUTION THEORY 



originate anew in a species, but must be derived directly or indirectly 

 from the sole basis which, in each species, forms the starting-point of 

 the individual — that is to say, in the Metazoa, from the germ-plasm 

 of the ovum. From it the determinant-complex of every regeneration- 

 rudiment must in the ultimate instance be derived. 



We may think of the matter thus : all the determinants of the 

 germ-plasm vary, grow slowly or quickly, and in certain circum- 

 stances may be doubled. In this way there arise what we may 

 call ' supernumerary ' determinants, which are not required in the 

 primary building up of the body from the ovum, and which may 

 remain in an inactive state in the nuclei of certain cells, ready to 

 become active under certain circumstances and to produce anew the 

 part which they control. Such "regeneration-idioplasm will at first 

 come to lie in the younger cells of the determinate organ, but it is 

 conceivable that under the influence of selection it may be gradually 

 shifted to other cells of a later developmental origin, or, conversely, 

 to others in a less external position, so that, for instance, the regen- 

 eration-rudiment for the finger of a newt may be contained not merely 

 in the cells of the hand, but in those of the fore-arm or even of the 

 upper arm. 



But all such segregation of determinant-groups cannot have taken 

 place, as we might perhaps be inclined to think, at the periphery in 

 the organ itself during its development; it must take place in the 

 germ-plasm of the ovum, for otherwise it could not be transmissible, 

 and could not be directed and modified by the processes of selection, 

 as is actually the case, as I shall show in more detail later on. 



I have already pointed out the importance of the role played 

 by liberating stimuli in regeneration, and not only of extra-organismal 

 stimuli, such as gravity, but above all of intra-organismal stimuli 

 that is, the influences exerted in a mysterious manner by other parts 

 of the animal on the parts which are in process of regeneration. It is 

 a great merit of the modern tendency in evolution theory that it has 

 demonstrated the importance of such internal influences. Although 

 we are still far from being able to define the manner in which these 

 influences operate, we may say so much, that it depends essentially 

 on the nature and extent of the loss which parts are reproduced by 

 the regenerating cells, and, also, on the position and direction of the 

 injured surface from which the regeneration starts. The influences, 

 still quite beyond our comprehension, which are exerted on the 

 regenerating part by the uninjured parts constitute the liberating 

 stimuli, which evoke the activity of one or other of the determinants 

 contained in the regeneration-idioplasm. 



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