74 THE GERiM-PLASM 



privilege of taking part in the formation of the organism, how 

 could one explain the existence of identical twins, about w^hich 

 we have received such valuable information from Galton him- 

 self ? How would it be possible for the exactly corresponding 

 gemmules in two individuals in the flying and ever-changing 

 swarm always to reach the most favourable position, even if the 

 ' stirp ' contained precisely similar gemmules ? 



In a subsequent section I shall attempt to show that this 

 struggle between homologous but individually different primary 

 constituents can be proved in quite another manner in connec- 

 tion with the idioplasm. It was necessary to mention Galton's 

 view here, in order to show that the forces of attraction and 

 repulsion, assumed by him, are introduced for an entirely 

 different purpose from that which I have stated with regard 

 to the similar forces in connection with the biophors of the 

 idio-plasm. 



Two physiological conditions of the elements of the idio- 

 plasm exist, — an active and an inactive. In the former, these 

 elements become disintegrated into their constituent parts ; 

 while in the latter, they remain entire, although they are capable 

 of multiplication. When determinants are active, they become 

 disintegrated into biophors, and are then capable of controlling 

 the cell in the nucleus of which they are situated. The activity 

 of entire ids depends on a disintegration into determinants, 

 which, though certainly successive, is often very slow; it must 

 be contrasted with the inactive state, which in both elements of 

 the idioplasm depends on the fact that their constituent parts 

 do not become separated from one another, but remain in their 

 primarily entire condition. In the immature ovum, for instance, 

 only 07ie kind of determinant — the 'oogenetic' determinant — is 

 active, and this controls the growth and histological difterentia- 

 tion of the egg ; all the other kinds remain inactive, as do also 

 the ids which are formed from them. Only when fertilisation 

 has occurred do they become active, — that is to say, one kind of 

 determinant after another begins to separate itself from the 

 entire id. We shall see later on, however, that ids of the germ- 

 plasm also exist which remain inactive even after fertilisation 

 has occurred, and are passed on from cell to cell in what we 

 may call an unalterable (^ gebu7idene)n^) condition, so as to form 

 subsequently the germ-cells of the embryo. We know as little 

 about the cause of this condition as we do about that of the 



