958 THE AMERICAN NATURALIST. |. [Vor. XXXV. 
example) changes over into a new, whole organism, leads us 
directly to the same conclusion. 
A ring cut at any level from the body of hydra closes its 
open ends quickly, and in the course of a few days it elongates 
and assumes the typical proportions of this form. At the 
time of the operation the piece was a part of a definite organi- 
zation, yet it afterwards becomes itself a whole structure. The 
material of which the piece is composed must be totipotent, since 
any piece may make a whole structure. The results demon- 
strate that although the piece must be regarded as a part of a 
whole organization before it was removed, yet after its removal 
it becomes itself a whole organism. This fact shows that there 
is no contradiction in our regarding the entire egg as also hav- 
ing a definite structure, or as being an organized whole, and yet 
any piece of it may become a new whole. This conclusion is 
of some importance because, at first, students of experimental 
embryology were inclined to go too far and assume that, since 
any piece of the egg could become a new whole, therefore, the 
egg itself must be regarded as a very simple structure. The 
experiments with hydra show that the egg may de as highly 
organized as is an adult animal, and yet a piece produce a new 
whole. It is scarcely necessary to add that the results do not 
show that the egg zs so highly organized but only that it may 
be thought to be so without contradicting the results of the 
experiments. 
I pointed out in my Woods Hole lecture of last year (1899) 
that from whatever part of the body a piece may be cut it will 
still be different in its different parts, in'so far as one part was 
nearer the anterior end and another nearer the posterior end of 
the animal. And similarly for the sides of pieces of a bilateral 
animal, one part will always have been nearer than another to 
the median plane, etc. These differences suffice, I think, for 
us still to form a causal conception of how the new axial rela- 
tions are attained, since the differences always present will be 
the basis on which the subsequent rearrangements take place, 
and the results of observations show, in fact, that the anterior 
end of the new organism comes from the anterior end of the 
pieces, etc. We may infer that a similar change takes place 
