ON CARYOKINESIS. 1/5 



identical by the means of observation at our disposal. 

 Thus, instead of inferring function from structure, we 

 infer structure from function and conclude that where- 

 ever we detect a difference in function the protoplasmic 

 structure must be different also. When, therefore, we 

 speak of the analysis of nuclear substances we do not 

 speak from actual knowledge of the substances thus 

 analyzed, but from purely scientific reasoning. 



It is probable that during cleavage, the original nuclear 

 substance may undergo a series of molecular changes, 

 and split up into a number of protoplasmic substances 

 each of a different molecular structure, and that as a 

 final result of this chain of metamorphoses different 

 kinds of tissue cells come into existence. In short, dif- 

 ferent morphological stages of the developing ovum may 

 be considered as so many different molecular conditions 

 of the protoplasm. And perhaps, the molecular consti- 

 tution of a dividing ovum in its earlier stage may differ 

 more from that of the later larval stasre than two or- 



O 



ganisms belonging to different species would differ from 

 each other in their adult condition. Professor Weis- 

 mann's phrase — ''ontogenetic stages of idioplasm" — 

 aptly expresses our meaning on this subject. For the 

 metamorphoses of structures and of embryonic tissues 

 must of necessity correspond to the change in the con- 

 stituent protoplasm. Without change in the nuclear 

 substance, development is impossible ; the Qgg must 

 remain an &gg forever. 



If all the determining elements of future tissues are 

 contained in the nucleus of the ovum, and if cleavage 

 is the process by which these elements are analyzed 

 into more tangible tissues, the question naturally arises 



