Form Regulation in Harenactis attenuata 383 
But whatever the factors involved the facts are of interest since 
they show a difference in localization, undoubtedly the result in 
some way of the experimental conditions, of the regulatory pro- 
cesses with respect to the wound. While such differences of local- 
ization are of frequent occurrence in plants and can often be con- 
trolled experimentally, they are much less common in animals. 
5 Correlations in the Formation of the Tentacle Groups 
While correlations are necessarily essential factors in the forma- 
tion of such systems as the tentacle groups, their effect is most 
conspicuous in certain particular features of these experiments, 
viz: in the formation of axially heteromorphic and radially hetero- 
morphic tentacles. In the first series, where the tentacle groups 
form on the line of union the symmetry of the groups is more or 
less perfectly completed by the formation of tentacles on the aboral 
side of the line of union opposite those on the oral side (Nos. I'to V, 
Figs. 6 to 20). In pieces where the oral and aboral ends close 
without uniting with each other tentacles never appear on the 
aboral ends, so far as my observations go, except in the cesophageal 
region, as already described. In all of the rings described, how- 
ever, not only the aboral but the oral ends as well are from the 
subcesophageal region, yet in all of the first series (Figs. 6 to 20) 
tentacles appear on what was originally the aboral end of the piece. 
The only sufficient reason for the appearance of axially hetero- 
morphic tentacles in the rings and not in other pieces involving 
the same region of the body is, in my opinion, the union of the 
aboral with the oral end in the rings. Apparently this union 
alters the character of the aboral end, at least quantitatively, so 
that it becomes capable of producing tentacles. Cases I and IU 
are particularly good illustrations of the influence of the oral upon 
the aboral end. In both of these cases (Case I, Figs. 6 and 8; 
Case III, Figs. 11 and 12) the tentacles appear first on the oral 
side of the line of union, 1. e., on the oral end, and later on the 
aboral side: Case II (Fig. 10) is similar to the other two but the 
early stages are not figured. Moreover, in these cases tentacles 
never appear at any point on the aboral end except opposite those 
