388 C. M Child 
following the wound. In the closure of the oral end of a piece in 
the usual manner (Child, ’oga) folds extending radially from the 
contracted cut end commonly occur and may pass through a region 
of tentacle-formation. In consequence of lack of distension, and 
perhaps also for other reasons, growth is retarded or inhibited 
in the fold, and in forms with delicate body-wall like Cerianthus 
zestruarli (Child, ’08) complete atrophy and degeneration of the 
folded or wrinkled regions may occur. Sometimes these folds 
involve a portion of the body-wall so large that the formation of 
one or more tentacles is inhibited or delayed. Cases of this sort 
in Cerianthus solitarius and C. membranaceous were described 
in an earlier paper (Child, ’o4, pp. 281 to 284, Figs. 5 to 7). On 
the other hand, very slight folds may divide a tentacle-forming 
region into two parts: localized growth may occur on each side of 
the fold, but growth in the fold itself is retarded or inhibited, 
consequently two tentacles begin to develop where only one would 
have formed if the fold had not been present. But in all the 
actinians which [ have used for experiment the increasing disten- 
sion following closure and mouth-formation and the gradual 
redifferentiation of the body-wall near the cut end usually bring 
about sooner or later the disappearance of these folds. In the 
case of folds dividing a tentacle-forming region the disappearance 
of the fold is followed by fusion of the two growing tentacles and 
their further growth as a single tentacle. Cases of this kind can 
often be observed in pieces undergoing regulation: they are not 
essentially different from other cases in which experimental divi- 
sion of the distal part of a regenerating primordium determines 
the differentiation of two structures instead of one, e. g., the star- 
fish arm and the amphibian leg. 
In the case of forked or branched oral-aboral tentacles on the 
rings the first factor mentioned, 1. e., the union of two tentacle- 
forming regions which are close together, in consequence of their 
increase in size, is probably more frequently concerned than the 
other. It is possible, however, that the cells immediately adjoin- 
ing the cut surfaces, 1. e., those cells which accomplish the union 
between oral and aboral ends in the rings react less readily, per- 
haps because of their exposure at the cut before union or for other 
