No. 420.] REGENERATION IN THE EGG. 961 
In regard to this latter point it seems that the development 
of an incomplete structure in Tubularia is not such an iso- 
lated phenomenon as it appears to be at first sight, but can be 
brought into harmony with certain other known results. For 
instance, when more than five segments are cut from the 
anterior end of the earthworm only five, as a rule, come back 
at whatever level of the anterior end the cut may be made. 
The amount of material that is formed at the cut-end, before 
differentiation begins, is about the same at all levels, and this 
gives, I believe, an insight into the phenomenon. There is for 
the earthworm, also, a lower limit of organization for the forma- 
tion of the head, or of a ring of the body, and the same new part 
is formed at each level, because the amount of material that is 
at first formed over the exposed end is the same. We must 
look upon this material as totipotent, but the number of rings 
that it produces is limited, on account of the amount of material 
present and of the necessary connection that exists between 
the lower limit of organization and the volume of matter! The 
analysis leads us in both cases to the supposition that the 
results are somehow dependent on the ultimate structure of 
the protoplasm from which arises the structure that we can 
see. The development of a proboscis from a small piece of 
the stem of Tubularia indicates that there is a quantitative ele- 
ment that comes into the problem, and this conclusion is directly 
in line with the conclusion that we reach from a study of pieces 
of minimal size of both adult organisms and of eggs. Below a 
certain point the organization of the protoplasm cannot take 
place, and it is this result that shows, I think, that we cannot 
look upon the whole as simply the sum total of similar parts, 
but as itself having a single plan of organization or structure. 
If we next proceed to an examination of the method of 
development of pieces of older embryos we find some further 
facts that bear on our problem. It has been found that if the 
hollow blastula of the sea-urchin be cut in two, the opening in 
for the same 
less rings. 
1 another 
1 The form of the new part must also be a factor in the problem, à 
amount of material, if of a different shape, might give rise to eos x 
The part of the body from which the new substance arises may be st 
factor, 
