HOMODYNAMIC AND HETERODYNAMIC DETERMINANTS 31 



to the same determinate X. Homologous determinants may be 

 either homodynamic or heterodynamic in their nature. Homo- 

 dynamic determinants are those which are quite identical with 

 each other. Heterodynamic determinants, on the other hand, 

 are those which have an idtimate or general identity, but whose 

 properties have no immediate identity. Thus, if we pair two 

 pigeons, and suppose the feathers on the wings of the one to 

 be pure white, the feathers on the wings of the other to be white 

 mingled with blue, the determinants of the purely white feathers 

 are said to be homodynamic with one another, both their im- 

 mediate identity (colour of the feathers) and their ultimate 

 identity (structure and composition) being obvious. On the 

 other hand, the determinants of the mingled white and blue 

 feathers are heterodynamic ; for, although the ultimate result of 

 their co-ordination be the same wing, there are differences which 

 manifest themselves in the varying of the colours. 



The composition of the germ-plasm, which we have just out- 

 lined, presupposes the existence of determinants as morpho- 

 logical and physiological units — as living units, in a word. 

 M. Yves Delage, in his great work on heredity, has maintained 

 that the theory of determinants assumes a too compUcated com- 

 position for the germinal substance, and he inclines to the view 

 that the germinal substance is extremely simple in its nature. 

 But, even if we pass over the fact that the protoplasm of the 

 Amoeba, which is one of the most elementary forms of life, is 

 already very compUcated in its nature ; we find that M. Delage 

 ascribes properties to the germinal substance which are difficult 

 to reconcile with his assumption of the simplicity of that sub- 

 stance. Thus he grants that the different groups of cells of the 

 hving organism, such as those of the muscles or the glands, are 

 contained in potentia in the parental germinal substance ; but 

 this is equivalent to postidating a system of determinants. And 

 if the determinants are not living autonomous units, but simply 

 particles of protoplasm, how can they resist the, assimilating 



