No. 420.] REGENERATION IN THE EGG. 969 
for those kinds of regeneration in which a new part is added at 
the end of the old part, and, as I have pointed out, it is not 
well suited to explain those cases in which a piece changes 
over entirely into a new whole. Since the development of 
parts of the egg and of isolated blastomeres and pieces of the 
embryo takes place by a process of morphallaxis, it is clear that 
the hypothesis is equally inapplicable to such cases. The kind 
of rearrangement or regulation that takes place in a piece of an 
egg, or of an isolated blastomere, or of a piece of a protozoón, so 
that a symmetrical whole is formed, cannot be made any clearer, 
I think, by the assumption of specific fluids or stuffs in the 
different regions that determine the later differentiation. 
The idea that there is a similarity between the process by 
which a broken crystal completes itself and that by which an 
animal ora plant may make good a lost part has often been 
suggested. The comparison rests, I think, on a superficial 
resemblance, and a careful examination of the nature of the 
two processes shows them to be the outcome of different fac- 
tors. It may, however, be asked in what respects is the mod- 
ern view of crystallization different from the view which I have 
advocated in regard to the reorganization of the protoplasm ina 
part of an egg or in a piece of hydra. Thetwo conceptions are 
in reality entirely different. A piece of a crystal does not rear- 
range its parts, much less its axes, to form a new whole of smaller 
size, but has deposited on its surface, from the saturated solu- 
tion in which it lies, new material that conforms in every respect 
to the original axes and planes. In a piece of an egg or of an 
animal, on the contrary, the entire old structure changes over 
into a new whole involving in some cases à change of axes. 
Pflüger's conception of the process Ub regenera aa gred 
points of resemblance to the idea of the recompletion of a 
crystal. He applies the conception, however, pre 
cases in which the regeneration is by a process of addition -: 
the old part (epimorphosis). Pflüger's hypothesis 15 that a t : 
cut-end the old material attracts from the blood new ma erial, 
ens : i rface and is there organized 
which is deposited over the cut-su d 
: ; : old part. He speaks of the 
at its region of contact with the ! pt UM hf with the 
new molecules being organized at the region 9 Pan 
