84 THE GERM-PLASM 



tiplication in the remaining determinants also diminishes, so 

 that the groups which they constitute gradually extend a less 

 distance into the ontogeny, until finally they drop out of it 

 altogether. 



It must not be understood that I have given a mechanico- 

 physiological explanation of the process of degeneration because 

 I have connected it with the theory of determinants. As long 

 as we know practically nothing about the forces which act 

 within and among the biophors, it will be impossible to offer an 

 explanation of this kind. I have only attempted to show that 

 this doctrine does not contradict the facts, but that, on the con- 

 trary, it agrees with them up to a certain point. The phenomena 

 of degeneration have not hitherto been considered from this 

 point of view. When a deeper insight into the actual phenomena 

 has been obtained, w^e may perhaps be able to make further 

 theoretical deductions, and it would then be possible to develop 

 the theory of determinants more fully. 



A few words may now be said as regards correlated varia- 

 tions. Darwin has shown what an important part these varia- 

 tions play in the transformation of species, and how changes 

 which we must consider to be primary are followed by a number 

 of others in various parts of the organism. Thus an increase in 

 size in a stag's antler necessitates a thickening of the skull, and 

 a strengthening of other parts, viz., the muscles of the neck, the 

 spines of the cervical vertebrae, the ligamentum nuchas, and 

 even the thoracic skeleton and fore-limbs. Referring all these 

 variations to the processes which take place in the idioplasm, 

 they will be seen to depend on changes in the corresponding 

 groups of determinants in the id of germ-plasm, which cannot 

 be due directly to the change and increase in the group of 

 determinants of the antler : thev must have arisen secondarilv, 

 owing to the occurrence of variations in the determinants upon 

 which selection could act. There is also an entirely different 

 kind of correlation, in which the variation in one part is accom- 

 panied by that in another, the latter having no anatomical or 

 functional connection with the former. Thus Darwin states, for 

 instance, that cats with blue eyes are generally deaf, and that 

 pigeons with feathered legs have a web between the outer toes. 



I do not think such correlations can be traced to a connection 

 of the parts by means of tlie nervous system : it is perhaps 

 more likely that they are due to the contiguity of the deter 7ninants 



