No. 420.] REGENERATION IN THE EGG. 965 
a new hydranth and stem.! The eggs produced by these forms 
are much smaller — hydra perhaps is to be excepted — than 
these minimal-sized pieces, and as the egg produces the typical 
form we cannot expect to find any agreement between the ulti- 
mate size of an isolated blastomere and of a piece of the adult 
that produces a whole structure. 
Peebles found that a smaller piece of a young bud than of the 
wall of hydra would produce a whole organism. The result is 
interesting inasmuch as the region where the bud appears is 
also a part of the wall. We find in a growing region of this 
sort that the protoplasm is denser than elsewhere, and may 
contain at first less water than other parts of the body, so that 
the absolute amount of living substance may be the same ina 
small piece of such a bud as is contained only in a much larger 
If this is true, and if the egg can 
piece of the wall elsewhere. 
r in its structure 
also be shown to contain relatively less wate 
than do other parts of the adult animal, it may still be possible 
that the amount of living substance necessary to give rise to 
the typical form may be found to be the same in the piece 
of the egg and of the adult. At present, however, we lack the 
data necessary to make the comparison. It is certain that in 
many forms — as for instance in the starfish — a piece of the 
adult that can regenerate the entire structure must be at least 
several thousand, perhaps million, times greater than the egg 
and must contain a much vaster amount of living substance. 
Many other factors than that of mere size must come into play 
in such cases, and it seems to me that the comparison 1S P 
after all, of much theoretical importance, since the method 3 
development of a piece of an €88 and of an adult may be 
. entirely different. 
Tubolars that a comparison is diffi- 
be 35 mm., then a piece of the stem 
hole; and pieces of this size pro- 
1 The length of the stem is so variable in 
Cult. If we assume the length of the stem to 
measuring 1 mm. in length is about zs of the w 
duced a new hydranth and stem. 
