No. 420.] REGENERATION IN THE EGG. 959 
in the reorganization of the egg; and we can form here also 
a causal conception of the change, although we may admit that 
it is a change different from anything that we know of in inor- 
ganic matter. . 
We may next èxamine some other results connected with 
the development of pieces of the adult and of the egg. It 
has been stated that a small piece of the stem of Tubularia 
sometimes produces only a partial form, — a proboscis, or a pro- 
boscis with reproductive organs, or a hydranth without a stem. 
The development of these partial structures occurs only in 
small pieces. The production of a proboscis, for instance, 
takes place only in pieces that are much smaller than the 
average size of the hydranth-forming region of a long piece of 
the stem. An entire hydranth without a stem may, however, 
develop from pieces that are much longer than the minimal 
size of the hydranth-forming region of short pieces. The point 
of special interest is that the development of the proboscis 
takes place in pieces whose material is totipotent, t.e., the 
material can produce any part of a hydranth or of a stem. 
We may restate the result by saying that there is a stronger 
tendency, especially in the more distal parts of the stem, to 
form the full-sized organs than to form the whole structure In 
a reduced form. 
These results with small pieces of Tubularia suggest at once 
a comparison with those cases in which a part of an egg 
develops into a part of an embryo, and not into a whole one of 
smaller size. This is most strikingly shown in the ctenophore 
egg and also in the egg of a snail, Ilyanassa. -It has been found 
that, if the first two or first four blastomeres of the ctenophore 
egg are isolated, each not only divides as à part, but each 
develops into an incomplete embryo that lacks, in the case 
of the one-half blastomere, a half or nearly half of the entire 
Structure, and in the isolated one-quarter blastomere lacks about 
three-fourths of the entire structure, etc. If Mss i 
from the fertilized but unsegmented egg of the same eS 
the embryos that develop from the nucleated pieces are a : : 
often incomplete. The results indicate that the phenomena us 
due to a lack of regulative power, or power of rearrangem 
