382 THE EVOLUTION THEORY 



of llu- nerve-cells of the brain requires the continual stimulus of the 

 hlood-streani, and cannot continue to exist without it; the specific 

 sensory-nerves and sense-cells of the eye, ear, olfactory oro-an, and so 

 on. are all ])ronipted to activity by adequate stimuli. The same is 

 true in reo^ard to the detenninants, they must be 'liberated' if they 

 are to distribute themselves and nn'orate into the cell-body ;' and we 

 have to ask how that happens, whether it is possibly due only to 

 their own internal condition, which a^'ain would, of course, depend 

 on the nutritive conditions of the cell in which they lie, or whether it 

 is perhaps due to some specific stinnilus which is necessary in addition 

 to the fact of ' maturit}^' just as a nuiscle is always ready to contract, 

 yi't only does so when it is affected by a specific stimulus. 



From the very first, therefore, I have considered whether it 

 would not be better to elaborate the determinant theory in such a way 

 that it would not be necessary to assume a disintegration of the id in 

 the course of ontogeny, but simply to conceive of every expression 

 of acti\dty on the part of a determinant as dependent on a specific 

 stimulus, which in many cases can only be supplied by a definite cell, 

 that is, by internal influences, and in other cases may be due to 

 external influences. 



Darwin assumed the first of these alternatives in his theory of 

 Pangenesis, which we have still to outline. In it he attributes to his 

 ■ gemmules ' the power of giving rise to particular cells, which, 

 however, they can only accomplish when they reach the cells which 

 are the genetic antecedents of those which the gemmules are to 

 control. Translated into the language of our theory this view would 

 read as follows : the whole complex of determinants is contained 

 Avithin every cell, as it is contained in the germ-cell, but at every 

 stage of ontogeny, that is, in each of the developing cells, only the 

 determinant which is to control the immediately successive cells is 

 ' liberated,' and that through the stimulus which the specific nature of 

 the cell supplies to the determinant. In that case there would 

 necessarily be in every species of animal as many specific stimuli 

 for determinants as there are determinants. This appeared to me 

 improbable, and I rejected the hypothesis because of the enormous 

 number of specific stimuli which it demands, but also on other grounds 

 which will be touched upon in the course of these lectures. 



Although the assumption of an autonomic dissolution of the 

 determinant complexes of the id in the course of ontogeny seems 

 to me imperative, I do not by any means reject the interposition 

 of liberating stimuli, indeed I regard their co-operation as indis- 

 pensable. Later on we shall discuss cases in which it is definitely 



