Form Regulation in H arenactts 67 
Complete Aboral Discs in the Hsophageal Region 
Pieces from the cesophageal region with a cut surface at each 
end often contract irregularly or so strongly that the cesophagus 
is more or less completely extruded from one end and closure is 
delayed or prevented: otherwise these pieces give the same results 
as those with cut surface at the aboral end only. In order to 
avoid these irregularities pieces including the original oral end of 
the animal and the old tentacles may be used, e. g., pieces includ- 
ing all of the region distal to the level b in Fig. 1. Such cesopha- 
geal pieces show a much higher death rate than pieces of equal 
size from other regions of the body. In my experiments 50 per 
cent or more of these pieces died without producing aboral tenta- 
cles. Pieces that remain in good condition for a week or more 
usually produce aboral tentacles. ‘These tentacles arise in the 
same manner as oral tentacles, but less rapidly. In general when 
a given level of the body, e. g., the level } in Fig. 1, forms the oral 
end of a piece, tentacles appear much more rapidly than when the 
-same level forms the aboral end of a piece. At the level 4, for 
example, oral tentacles usually became visible in my experiments 
about forty-eight hours after section, while aboral tentacles appear 
after six days or more. 
The heteromorphic tentacles may reach a length of eight to 
ten millimeters and would undoubtedly become longer, were it 
not for the fact that the distension in these cesophageal pieces grad- 
ually decreases until they are completely collapsed, after which 
death soon occurs. As the distension decreases the original oral 
tentacles undergo gradual decrease in size and atrophy at the tips 
until they are the same size as the aboral tentacles: in later stages 
the aboral tentacles also undergo decrease and atrophy as the dis- 
tension decreases still further, until both oral and aboral tentacles 
may be reduced to short stumps. In general the history of these 
cesophageal pieces is similar in Harenactis and Cerianthus (Child, 
’04) except that in Cerianthus heteromorphosis has been observed 
only very rarely (Child, ’o5). 
Fig. 2 shows a diagrammatic longitudinal section of an cesopha- 
geal piece with heteromorphic tentacles. At the stage figured the 
