38 THE EVOLUTION THEORY 



of equivalent portions of germ-plasm, each of which contains all 

 the kinds of determinants appertaining to the Ijuilding up of 

 an individual, but each of these kinds in a particular individual 

 form. I have already called these ids 'ancestral plasms,' and 

 the term is appropriate, in so far that in every fertilization an 

 equal number of ids from the father and from the mother are 

 united in the ovum, so that the child is built up of the ids of his 

 two nearest 'ancestors.' But as the ids of the parents are derived 

 from those of the grandparents, and these again from those of the 

 great-grandparents, the ids are in truth the idioplasm of the 



ancestors. 



The expression, how^ever, has been very frequently misunder- 

 stood, as if it were intended to mean that the ids retained unchanged 

 for all time the character of their respective ancestors, and I have 

 even been credited with supposing that our own ids still consist 

 of the determinant-complexes of our fish-like or even Amceba-like 

 ancestors. But in reality no id exactly or completely corresponds 

 to the type, that is, to the whole being of any one of the ancestors 

 in whose germ-plasm it was formerly contained, for each of the 

 ancestors had many ids in his germ-plasm, and his entire constitution 

 was not determined by any one of these alone, but by the co-operation 

 of them all. The individual arising from a germ-cell must necessarily 

 be the result of all the ids which make up his germ-plasm, but 

 undoubtedly the share taken by some of them may be much stronger 

 than that taken by others. It is also clear that, if we leave out 

 of account any possible variation on the part of the ids, each of them 

 belongs, not to one ancestor only, but to a whole series of ancestors, 

 and must have taken part in their development, so that it is not 

 the idioplasm of any particular ancestor, but only ancestral plasm 

 in the general sense. In this sense we may quite well retain the 

 designation, ' ancestral plasm,' for the id. 



Thus, according to our view, the germ-plasm consists of ids, 

 each of which contains all the determinants of the whole ontogeny, 

 but usually in individually different quality. 



Returning for a moment to the processes by which the reduction 

 of the chromosomes, that is, of the nuclear rods of germ-plasm in 

 the ovum and sperm-cell is brought about, we recall the fact that 

 this happens at the last two divisions of the germ-cell, the so-called 

 'maturing divisions.' In these the nuclear substance, as we liave 

 seen, is divided between the two daughter-nuclei in a manner quite 

 different from the usual one, for a longitudinal splitting of the rods, 

 bands, or spheres in i\\Q equatorial plane of the nucleus does not 



