Form Regulation in Harenactis 73 
evident from Fig. 10. In all cases of this kind both the old ten- 
tacles distal to the incision and the new aboral tentacles undergo 
atrophy and the whole region disappears because the mesenterial 
ostia are always proximal to the incision, and this region, therefore 
does not share in the distension of other parts of the body (Child, 
’oga). ‘The atrophy at the tip of the old tentacles is shown in Fig. 
TL: ‘ 
All possible gradations between the condition represented in 
Fig. 11 and the usual condition (Figs 4 and 5) can be obtained 
according to the degree of invagination existing at the time the 
incision is completed. Attention may again be called to the fact 
that in all such cases the new tentacles appear in the same relation 
to the cut surfaces, though their space relations to other parts may 
differ widely. 
2 Aboral Restitution in the Subzsophageal Region 
Under certain special conditions to be described in a later section 
heteromorphic tentacles may appear in regions aboral to the cesoph- 
agus, but where the closure of the wound occurs in the usual man- 
ner, 1. e., by approximation of the parts of the aboral cut surface 
of the body-wall and the formation of new tissue between them, 
as described in the preceding paper, tentacles have never been 
observed at the aboral end. 
Even when the level of section is immediately proximal to the 
cesophagus (c, Fig. 1) closure occurs to form an aboral end, at 
least so far as appearance is concerned. A’sophagus and body- 
wall never unite with each other unless a cut surface is present on 
each: moreover, these two surfaces must be connected by contin- 
uous cut margins of mesenteries in order that such union may 
occur. These conditions exist only when the section involves 
the cesophagus, never when the level of section lies aboral to the 
cesophagus. 
Section at any level proximal to the cesophagus is followed by 
closure of the aboral end, though the closure may be more or less 
delayed by protruding muscles and mesenteries. Nooutgrowth 
of a new aboral end such as is found in Cerianthus solitarius 
