Form Regulation in Harenactis attenuata a5 
new organization than others, provided they still remain capable 
of reacting to the factors which determinethenew result. Itseems 
probable then, not only from observation, but on general grounds 
as well, that the more complete removal of the old mesenteries 
from particular regions about the circumference of the oral end 
of a piece which forms a ring may constitute an important factor 
in determining the localization of tentacle groups at those regions. 
That this is the only factor involved, | should certainly not ven- 
ture to assert at present. Evidently the union of oral with aboral 
end not only decreases polarity but also decreases or eliminates 
the correlations about the circumference so that different regions 
of the circumference react independently, at least in considerable 
degree. Whether a difference in growth activity is sufficient to 
accomplish this cannot be determined at present. From my pre- 
vious experiments on actinians it is evident that different parts 
of the circumference are not normally very closely correlated, for 
each part performs its characteristic reaction according to the 
conditions present at that point and apparently without reference 
to other parts. The results of the lateral incisions which have been 
described both for Harenactis and Cerianthus indicate this very 
clearly. ‘This being the case [ am inclined to believe that the 
establishment of a region of more rapid growth and less differen- 
tiation at a certain point of the circumference might be sufficient 
to determine reaction of that region independently of other parts 
about the circumference. 
If these suggestions are correct they afford some basis for under- 
standing how it is that a number of isolated groups of tentacles 
may appear about the circumference of these rings. Perhaps 
other internal factors of which we know nothing are involved, but 
it is evident that such factors if present act in very indefinite and 
irregular manner, since restitution in rings varies from mere 
closure without the formation of tentacles at all to the formation 
of anywhere from one to six—the maximum number in my experi- 
ments, though doubtless not the maximum number possible— 
groups of tentacles in which the number and arrangement of the 
tentacles may also vary greatly. In short the determining factor 
or group of factors in the localization is very evidently what we 
