THE FACTS AND FUNCTION OF SEX 27 



But in higher animals, and notably in most plants, 

 the reproductive cells cannot be recognised until the 

 development of the organism is considerably ad- 

 vanced. In such cases, then, it is impossible to 

 demonstrate any continuity between the germ-cells 

 of an individual and the germ-cells of its parent. 

 But Weismann has shown that it is not therefore 

 necessary to abandon the invaluable concept of 

 continuity. He very reasonably assumes that the 

 essential part of each germ-cell is not, for instance, 

 the cell-membrane, or the cellular shape, but a par- 

 ticular kind of living matter — the germ-plasm. He 

 supposes, then, that in the development of each 

 individual a portion of the germ-plasm contained in 

 the parental ovum "is not used up in the formation 

 of the offspring, but is reserved unchanged for the 

 formation of the germinal cells of the following 

 generation," There are grounds for believing, as we 

 shall see, that the chromatin of the nuclear network 

 represents this germ -plasm. Though there is not 

 always continuity of germ-cells from generation to 

 generation — as there demonstrably is in many animals 

 — there is always, in all the animals and plants which 

 display this mode of reproduction, a " continuity of 

 the germi-'plasm" 



This phrase must be remembered. It expresses a 

 theory of the very highest importance ; it is sup- 

 ported by a large amount of evidence, and is posi- 

 tively contradicted by none ; ^ it illuminates all our 

 conceptions of inheritance ; and the inferences from 

 it are of the first importance in regard to the great 

 controversy as to the inheritance of acquirements. 

 1 See Chapter IX. " The Theories of Heredity." 



