No. 420.] REGENERATION IN THE EGG. 955 
substances of the protoplasm; but after the piece has been 
divided into parts or cells the contents of each cell is separated 
from that of its neighbor by the cell-walls which we have come 
to look upon as barriers preventing free interchange between the 
cells. In many cases, however, an actual continuity of the pro- 
toplasm from cell to cell has been demonstrated, and it has been 
recently shown that connections may be established during the 
cleavage period between neighboring cells. We shall not go 
far wrong, I think, if we assume that the protoplasm through- 
out the embryo is a continuous structure, and that it is not 
shut up in protoplasmic-tight compartments. How, then, from 
this point of view can we look upon the changes that take 
place in an unsymmetrical piece so that it becomes symmet- 
rical? Can we regard the first step to be the same as in the 
piece of an egg, Ze, to be the outcome of a symmetrical rear- 
rangement of the material or substances contained in the 
egg? We may think of this as possible, but the change in itself 
would not be sufficient to account for the subsequent events, 
unless we assume that it leads to the symmetrical organization 
of the living substance itself, for on this rather than on the 
gross contents of the protoplasm the subsequent changes seem 
to depend. That this must be so is shown, I think, by the 
following considerations. 
Numerous experiments have demonstrated that any part of 
the egg may produce a whole embryo — provided, of course, 
that it contains the nucleus and is large enough. The sub- 
stances contained in the different parts of the protoplasm are 
very similar throughout the egg, although there may be mov 
orless of one or of another sort in each region. Since any 
part of the egg can produce an embryo we cannot regard 
the presence or absence of any of these substances as of fun- 
damental importance; hence it is probable, I think, that the 
result depends on the protoplasm rather than on the substances 
it contains. i * 
The structure of the egg is à symmetrical ory d 
development shows; a piece of the egg retains at Bre T "e 
Structure in most cases as its cleavage demonstrates, spe 
may later become also symmetrical, as the later changés 
