Production of New Hydranths in Hydra 13 
was absorbed and no regeneration took place. The length of 
time necessary for regeneration to be far enough along for a piece 
of the regenerating tissue to call forth a hydranth from the stock 
when grafted, would of course depend on the rate of regeneration 
from an exposed surface, and this has been found to vary in differ- 
ent regions of the body. If, therefore, the original cut were made 
just below the tentacles instead of in the middle of the body, less 
than ten hours would probably suffice for the regenerating tissue 
when grafted to call forth a new hydranth from the stock. 
Group H 
Tissue of Bud as Graft 
In this experiment, a small piece of the anterior end of a young 
bud whose tentacles had not yet been formed, was cut off and 
grafted into the middle of the body of a stock hydra. There 
followed as a result of the graft an outgrowth of a new hydranth 
similar to that instigated by the insertion of regenerating tissue into 
the stock (Figs. 40, 41). That this outgrowth was a new hydranth 
and not an ordinary bud is shown by the length of its tentacles. 
These were long like those of a hydranth and not short like those 
of a bud (cf. Figs. 41 and 8.) 
General Conclusions to Part I 
The conclusions to be drawn from the whole set of experiments 
are as follows. A new hydranth can be formed by a hydra in any 
part of its body except in the tentacle region, when the necessary 
stimulation is given by a grafted piece. ‘The stimulus can be given 
by no other grafted piece than the material that lies at the base 
of the free tentacles, or that lies in a regenerating hydranth or a 
bud. The transformation of body wall material into hydranth 
material depends therefore not on the size of the piece grafted into 
it, but entirely on the differentiation of the grafted material. If 
the material grafted has been entirely differentiated into material 
lying at the base of a tentacle, or if it has been sufficiently differen- 
tated by regeneration or budding into this kind of material, this 
