Form Regulation in Harenactis attenuata 3609 
of growth. Concerning the nature of these only surmise is pos- 
sible. It is perhaps worth while however, to call attention to one 
point: from certain of my observations on regulating actinians it 
has seemed probable to me that the so-called ingrowth of the cesoph- 
agus is not actually so much an ingrowth as a growth in the oral 
direction of the structures about the cesophagus and of the cesopha- 
gus itself, i. e., the mouth-opening forms on the disc and growth 
of all parts in the oral direction brings about the formation of the 
cesophageal tube, the original mouth-opening being at its aboral 
end. In the case under consideration almost no growth of the 
small discs occurs after the formation of the tentacles. If the 
above suggestions as to the method of cesophageal development 
are correct the localization of a region of growth where the cesopha- 
gus usually forms might perhaps result in an outgrowth as in this 
case. [his suggestion may or may not be correct. 
This is the only case in which structures which might possibly 
represent the cesophagus are formed. The only reason for the 
presence of such structures in this case and their absence in others 
which suggests itself is that perhaps in the present case the regu- 
latory tentacle-groups represent something a little nearer to a 
normal oral end than in the other cases. ‘There are several fea- 
tures which indicate that such may be the case; in the first place 
the symmetry of the groups and the equal length and simultan- 
eous appearance of the tentacles constitute a marked difference 
from all other cases except perhaps No. VIII; secondly, exami- 
nation of these groups showed what seemed to be new mesenteries, 
radially arranged and apparently quite distinct and separate from 
the old mesenteries. [In some of the cases previously described 
new mesenteries were apparently present about a part of the 
circumference of the group but in this case all were apparently 
new. If these observations are correct it appears probable that 
the five groups of tentacles under consideration do perhaps _rep- 
resent a somewhat closer approach to normal oral ends than 
other cases and this difference may determine the establishment of 
an cesophageal region of growth in these groups and its absence 
in the others. 
After two weeks this ring gradually collapsed and the tentacles 
