Form Regulation in Harenactis 77 
often does attachment of the aboral end thus formed occur. Pieces 
like Fig. 12 have never been observed to attach themselves and 
often pieces comprising almost the whole length of the body do 
not, but my notes record the occurrence of attachment more fre- 
quently in longer than in shorter pieces. The question of the 
localization of the power of attachment was discussed in my earlier 
paper (Child ’o8b, p. 11): I need mention here only that it is 
more marked toward the proximal end and that its limits appar- 
ently differ more or less widely according to conditions. 
3 Analysis of the Experimental Data with Reference to the 
Regional Factor 
The facts are briefly as follows: at all levels within the cesopha- 
geal region restitution from an aboral cut surface results in the 
formation of structures normally characteristic of the oral end; 
when the operation involves the whole cross-section of the body a 
complete disc with twenty-four tentacles is formed similar to that 
at the oral end, and when incisions involving only a part of the 
circumference are made partial discs with tentacles correspond- 
ing in number to the number of intermesenterial chambers cut 
across by the incision are formed. At all levels proximal to the 
cesophageal region aboral restitution results in the formation of 
structures normally characteristic of the aboral end, though en- 
vironmental conditions may prevent complete restitution of the 
parts removed. The formation of heteromorphic structures 1s 
then limited to the cesophageal region in the cases under con- 
sideration. 
This definite localization of heteromorphosis may apparently 
be determined by one or both of two possible regional factors or 
factor-complexes, viz: first, the physiological character or consti- 
tution of the cesophageal and subcesophageal regions and, secondly, 
the method of closure of the aboral end in the two regions. My 
experiments show clearly that external factors are not concerned. 
As regards the first of these factors, the physiological character 
or constitution, it is evident that the formation of heteromorphic 
discs and tentacles would be impossible if the parts concerned did 
