74 C. M. Child 
(Child ’03, pp. 257 to 259) ever occurs, but the area of new tissue 
enlarges somewhat as the body becomes distended after closure. 
The actual restitution of the aboral portions removed is accom- 
plished, so far as it occurs, by the gradual growth and redifferen- 
tiation of the more proximal portions of the piece. 
Fig. 12 Restitution in a piece including the whole cesophageal region. 
The question as to whether complete aboral restitution occurs 
at all levels of the body requires some consideration. Fig. 12, 
for example, represents the distal piece resulting from section of the 
body at the level c, Fig. 1. In this case practically the whole 
region containing the retractor muscles has been removed and the 
piece represents little more than the cesophageal region. Such 
pieces may live for months without food, though they of course 
decrease in size. During this time the cesophageal region increases 
somewhat in length, but never attains anything like the usual pro- 
portions, at least never within the four and a half months over 
which my observations extended. Restitution of the retractor 
muscles in such individuals does not occur to any great extent 
and they remain wholly incapable of invagination. Moreover, 
I have never observed attachment to the substratum by the aboral 
end in these cases. 
There can be little doubt that the absence or small amount of 
aboral restitution in these cases is, at least in large part, the con- 
sequence of the conditions of existence. In an earlier paper 
(Child, ’o8b) I described certain regulatory changes in shape and 
structure which occurred when the animals were kept for long 
