THE BEARERS OF THE HERITAGE 309 



in that body are not identical now becomes obvious. P'or in sucli 

 cases as those just cited one sees the germinal substance which is to 

 carry on the race set aside at an early period in a given individual; it 

 takes no part in the formation of that individual's body, but remains 

 a slumbering mass of potentialities which must bide its time to awaken 

 into expression in a subsequent generation. Thus an egg does not 

 develop into a body which in turn makes new germ-cells, but body and 

 germ-cells are established at the same time, the body harboring and 

 nourishing the germ-cells, but not generating them. The same must 

 be true also in many cases where the earliest history of the germ-cells 

 cannot be visibly followed, because in any event, in all higher animals, 

 they appear long before the embryo is mature and must therefore be 

 descendants of the original egg-cell and not of the functioning tissues 

 of the mature individual. This need not necessarily mean that the 

 germ-cells have remained wholly unmodified or that they continue 

 uninfluenced by the conditions which prevail in the body, especially 

 in the nutritive blood and lymph stream, although as a matter of fact 

 most biologists are extremely skeptical as to the probabiUty that 

 influences from the body beyond such general indefinite efi"ects as 

 might result from under-nutrition or from poisons carried in the blood, 

 modify the intrinsic nature of the germinal substances to any measur- 

 able extent. 



Germinal continuity. — The germ-cells are collectively termed the 

 germinal protoplasm and it is obvious that as long as any race continues 

 to exist, although successive individuals die, some germinal protoplasm 

 is handed on from generation to generation without interruption. 

 This is known as the theory of germinal continuity. When the organ- 

 ism is ready to reproduce its kind the germ-cells awaken to activity, 

 usually undergoing a period of multiplication to form more germ-cells 

 before finally passing through a process of what is known as matura- 

 tion, which makes them ready for fertilization. The maturation 

 process proper, which consists typically of two rapidly succeeding 

 divisions, is preceded by a marked growth in size of the individual cells. 



Individuality of chromosomes. — Before we can understand fully 

 the significance of the changes which go on during maturation we shall 

 have to know more about the conditions which prevail among the 

 chromosomes of cells. As already noted each kind of animal or plant 

 has its own characteristic number and types of chromosomes when 

 these appear for division by mitosis. In many organisms the chromo- 

 somes are so nearly of one size as to make it difficult or impossible to 



