950 THE AMERICAN NATURALIST. [Vor. XXXV. 
It has been only within the last few years that zoólogists 
have discovered that parts of the embryo, or even of the unseg- 
mented egg, have also the power of producing new, whole 
organisms, and while this process has been here and there 
brought into relation with the process of regeneration, — espe- 
cially by Roux and by Barfurth, — yet up to the present time 
no systematic analysis has been carried out in order to see 
how far the regeneration of pieces of an adult organism and 
of pieces of the egg are similar or identical processes. It is 
the special object of this paper to examine further into this 
question. 
L 
In order to make clear our subsequent comparison between 
the development of pieces of the adult and of the egg and 
embryo it will be necessary in the first place to review briefly 
a few well-known facts. It has been stated that there are, in 
general, two modes by which a piece of an adult may regener- 
ate: (4) either by the development of new tissue at the 
exposed regions, — epimorphosis; or (2) by transformation of 
the old part into a new form, — morphallaxis. 
(4) a. Furthermore, we find under the first category that 
when a small piece of the organism is removed (1) the organ- 
ism regenerates as much as is lost ; but (2), on the other hand, 
the small piece does not generally make the whole organism, 
if in fact it regenerates at all. As examples of these different 
processes I may cite the following cases. If the leg is cut 
from a newt, the larger piece — the newt — makes a new leg, 
but the leg does not make a new newt. If the head is cut 
from a snail, the snail makes a new head, — if the cut has 
not been made too far back, — but the head does not make a 
new snail. If it be objected that in both cases the smaller 
piece dies before regeneration can begin, I may cite another 
experiment made on the earthworm. If a few anterior seg- 
ments are cut off, they do not make a new worm, although the 
piece may remain alive for a long time without showing any 
signs of regeneration, and during this time the larger piece, 
from which the anterior end had been cut off, may have 
