FOUNDATION OF A THEORY OF HEREDITY. 213 



For if the specific mole'cular structure of a cell-body is caused 

 and determined by the structure of the nucleoplasm, every kind 

 of cell which is histologically differentiated must have a specific 

 nucleoplasm. But the egg-cell of most animals, at any rate during 

 the period of growth, is by no means an indifferent cell of the 

 most primitive type. At such a period its cell-body has to 

 perform quite peculiar and specific functions ; it has to secrete 

 nutritive substances of a certain chemical nature and physical con- 

 stitution, and to store up this food-material in such a manner 

 that it may be at the disposal of the embryo during its develop- 

 ment. In most cases the egg-cell also forms membranes which 

 are often characteristic of particular species of animals. The 

 growing egg-cell is therefore histologically differentiated : and 

 in this respect resembles a somatic cell. It may perhaps be com- 

 pared to a gland-cell, which does not expel its secretion, but 

 deposits it within its own substance 1 . To perform such specific 

 functions it requires a specific cell-body, and the latter depends 

 upon a specific nucleus. It therefore follows that the growing 

 egg-cell must possess nucleoplasm of specific molecular struc- 

 ture, which directs the above-mentioned secretory functions of 

 the cell. The nucleoplasm of histologically differentiated cells 

 may be called histogenetic nucleoplasm, and the growing egg- 

 cell must contain such a substance, and even a certain specific 

 modification of it. This nucleoplasm cannot possibly be the same 

 as that which, at a later period, causes embryonic development. 

 Such development can only be produced by true germ-plasm 

 of immensely complex constitution, such as I have previously 

 attempted to describe. It therefore follows that the nucleus of 

 the egg-cell contains two kinds of nucleoplasm : germ-plasm 

 and a peculiar modification of histogenetic nucleoplasm, which 

 may be called ovogenetic nucleoplasm. This substance must greatly 

 preponderate in the young egg-cell, for, as we have already seen, 

 it controls the growth of the latter. The germ -plasm, on the 

 other hand, can only be present in minute quantity at first, but 

 it must undergo considerable increase during the growth of the 

 cell. But in order that the germ-plasm may control the cell- 



[' Such gland-cells are known in both animals and plants. See W. Gardiner and 

 Tokutaro Ito, On the structure of the mucilage-secreting cells of Bleclmum occidentale 

 L., and Osmunda regalis L., ' Annals of Botany,' vol. i. p. 49. S. S.] 



