No. 420.] REGENERATION IN THE EGG. 967 
determine the differentiation of the cell. In other words, 
the protoplasm is looked upon as a kind of indifferent medium 
on which the nuclear germs feed and multiply, and, replacing 
the protoplasm of each cell, produce there their particular 
product. 
In order to account for the regeneration of parts of the adult 
itis assumed that there has taken place during development 
not only an unraveling of the qualities of one germ, but at the 
same time at each or many of the divisions of the nucleus a 
quantitative division of another original whole germ, or later of 
a part of that germ, into like parts. This second germ is a sort 
of reserve stuff for future contingencies, and during regeneration 
this reserve stuff is supposed to become active and to do what 
is required of it. Pieces of the egg or of the embryo are also 
supposed to be able to regenerate, owing to the presence of 
this reserve idioplasm or germ in each nucleus, that is awakened 
into activity by the injury to the whole and then proceeds by 
qualitative division of exactly the right sort to set free the 
necessary germs to complete the embryo. 
I need not repeat here the many objections that have been 
brought forward in opposition to Weismann's view, or stop to 
point out how the upholders of this view have been obliged 
again and again to add subsidiary hypotheses to meet the 
objections that have appeared, but I may indicate at least some 
of the difficulties that this view meets with from the point of 
view of regeneration in the egg and embryo. 
The hypothesis assumes that at each division of the egg a 
sorting out of the qualities of the embryo takes place. Obser- 
vation shows, however, that at each division there is an equal 
division of the chromatin, and not an unequal division, as would 
necessarily take place in some of the divisions, if the hypothesis 
is correct. The experiments with the ctenophore egg indicate 
that the protoplasm is an important factor in the early divi- 
sions. The experiment of compressing the frog's egg during 
its period of division, so that a distribution of the nuclei in the 
protoplasm, different from that in the normal egg, is brought 
about, indicates that the early nuclei are equivalent ; and the 
development into whole embryos of pieces of the egg 1n which 
