IV.] FOUNDATION OF A THEORY OF HEREDITY. 1 93 



the cell-body which surrounds the polar globules Q){ Amphorina 

 is, as a matter of fact, somewhat larger than the sphere of 

 green cytoplasm which surrounds the nucleus of the egg ! 

 The difference between the polar bodies and the egg-cell can 

 thus only be explained on the supposition that, in the division 

 of the nuclear spindle, two qualitatively different daughter- 

 nuclei are produced. 



There does not seem to be any objection to the view that 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 &^g 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, becomes more complicated according to the greater 

 complexity of the organism developed from it, then the follow- 

 ing 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 contains the whole of the 

 ectoderm, possesses a more complicated molecular structure 

 than that of a single epidermic cell or nerve-cell. These con- 

 clusions will be admitted when it is remembered that every 



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