22O EDWIN G. CONKL1N. 



derived from the nucleus, the first from the nucleus of the oocyte, 

 the last two from the nucleus at the last oogonic division. 



This remarkable condition in which considerable portions of 

 the ooplasm can be traced back to the nucleus is of the greatest 

 theoretical importance. From all sides the evidence has accu- 

 mulated that the chromosomes are the principal seat of the in- 

 heritance material until now this theory practically amounts to a 

 demonstration. On the other hand all persons who have much 

 studied cell-lineage have been impressed with the fact that polar- 

 ity, symmetry, differentiation and localization are first visible in 

 the cytoplasm and that the positions and proportions of embry- 

 onic parts are dependent upon the location and size of certain 

 blastomeres or cytoplasmic areas. However in the fact that 

 large quantities of "nuclear sap" containing dissolved oxychro- 

 matin escape into the cell body at every mitosis (i>. Conklin, 1902) 

 and that these nuclear substances then contribute to the formation 

 of specific organ-forming substances of the cytoplasm we see a 

 possible means of harmonizing the facts of cytoplasmic organiza- 

 tion with the nuclear inheritance theory. 



TYPES OF GERMINAL ORGANIZATION. 



By those who maintain the view that the egg 'is typically com- 

 posed of "simple undifferentiated protoplasm" the remarkable 

 organization of the ascidian egg will probably be regarded as an 

 extreme case of precocious differentiation. This may perhaps be 

 the case but the fact that germinal differentiations 'and localizations 

 occur in the eggs of annelids, mollusks, nemerteans, echinoderms, 

 ctenophores, nematodes and ascidians shows that it is by no means 

 a rare phenomenon and it really seems as if the burden of proof 

 were shifted to those who maintain that the egg is typically un- 

 differentiated. Unquestionably the egg is less highly differenti- 

 ated than the embryo or larva, as organ-forming substances are 

 simpler than the organs to which they give rise, but the evidence 

 drawn both from observation and experiment shows conclusively 

 that in a large number of animals the substances of the egg are 

 not homogeneous nor equipotential. But even granting that 

 there are cases in which there is no such differentiation of the 

 ooplasm, this supposed lack of differentiation can apply only to 



