190 THE CONTINUITY OP THE GERM-PLASM AS THE 



microsomata of the nuclear loops assuming that these bodies 

 represent the idioplasm are capable of dividing into halves, equal 

 in form and appearance, but unequal in quality. We know that 

 this very process takes place in many egg-cells ; thus in the 

 egg of the earth-worm the first two segmentation spheres are 

 equal in size and appearance, and yet the one forms the endoderm 

 and the other the ectoderm of the embryo. 



I therefore believe that we must accept the hypothesis that, 

 in indirect nuclear division, the formation of unequal halves may 

 take place quite as readily as the formation of equal halves, and 

 that the equality or inequality of the subsequently produced 

 daughter-cells must depend upon that of the nuclei. Thus during 

 ontogeny a gradual transformation of the nuclear substance takes 

 place, necessarily imposed upon it, according to certain laws, by its 

 own nature, and such transformation is accompanied by a gradual 

 change in the character of the cell-bodies. 



It is true that we cannot gain any detailed knowledge of the 

 nature of these changes in the nuclear substance, but we can very 

 well arrive at certain general conclusions about them. If we may 

 suppose, with Nageli, that the molecular structure of the germ- 

 idioplasm, or according to our terminology the germ-plasm, be- 

 comes more complicated according to the greater complexity of 

 the organism developed from it, then the following conclusions will 

 also be accepted, that the molecular structure of the nuclear 

 substance is simpler as the differences between the structures 

 arising from it become less ; that therefore the nuclear substance 

 of the segmentation-cell of the earth-worm, which potentially con- 

 tains the whole of the ectoderm, possesses a more complicated 

 molecular structure than that of a single epidermic cell or nerve- 

 cell. These conclusions will be admitted when it is remembered 

 that every detail in the whole organism must be represented in 

 the germ-plasm by its own special and peculiar arrangement of the 

 groups of molecules (the micellae of Nageli), and that the germ- 

 plasm not only contains the whole of the quantitative and qualita- 

 tive characters of the species, but also all individual variations 

 far as these are hereditary : for example the small depression 

 belti the centre of the chin noticed in some families. The physical 

 manyses of all apparently unimportant hereditary habits or struc- 

 , of hereditary talents, and other mental peculiarities, must 



