REPRODUCTION. 657 



organising part of the protoplasm he considers to be a part 

 of the Stereoplasm, which he terms Idioplasm; the rest 

 of the protoplasm he regards as being simply nutritive. He 

 conceives of the idioplasm as forming a continuous network 

 throughout the organism, but its properties are not the same 

 in all parts, the differences being, not of a material, but of a 

 dynamical nature. The idioplasmic network of the adult 

 organism has been gradually formed by growth from the 

 idioplasm of the spore: the idioplasm of the spore is the 

 microcosmic image of the macrocosmic organism. Repro- 

 ductive cells are formed by the return of portions of the 

 somatic idioplasm to the condition of the idioplasm of the 

 spore from which the organism sprang, in a word to the 

 embryonic condition, the return consisting in a dynamical 

 change. A complete reproductive cell, that is, a spore, con- 

 tains just so much idioplasm, and that in the same condition, 

 as did the spore of the previous generation; incomplete 

 reproductive cells, that is, gametes, contain a smaller amount 

 of embryonic idioplasm than this, and hence comes the 

 necessity for a sexual process. The sexual process takes 

 place in virtue of a specific attraction between the gametes of 

 the two sexes, and consists in the fusion of the idioplasm 

 of the two cells. Naegeli leaves it an open question whether 

 this fusion is material, or, as it were, dynamical, but he 

 distinctly inclines to the latter alternative. Heredity de- 

 pends upon a transmission of the properties of the idioplasm. 

 The law of heredity is the analogue of the physical law of 

 inertia. Just as a body in motion continues to move in 

 the same direction and with the same velocity unless acted 

 upon by some external force, so the dynamical condition 

 of the idioplasm of the parents is continued in the children. 

 But the return of the somatic idioplasm of the parent, in 

 the formation of reproductive cells, to the embryonic con- 

 dition of the spore from which the parent sprang is not 

 exact; so that the offspring never quite resemble their 

 parent or parents. Hence comes variation. The difference 

 between offspring and parents which is due, on Naegeli's 

 assumption, to inherent variability, is the expression of the 

 V. 42 



