Form Regulation in Harenactis 79 
Clearly then the experimental evidence leads us to the conclu- 
sion that no essential qualitative axial, 1. e., polar, differences in 
constitution exist in the cesophageal region of Harenactis. Quan- 
titative axial differences undoubtedly do exist, as is shown by 
the fact cited in the preceding paper (Child, ’ogb) that even in the 
cesophageal region the rapidity of tentacle-formation at the oral 
ends of pieces decreases with increasing distance of the level of 
section from the original oral end. Moreover, aboral tentacles 
appear much later than oral tentacles at the same level, as was 
noted above in the present paper. This retardation of aboral 
tentacles as compared with oral at the same level cannot be due 
to preéxisting and persisting quantitative axial differences, since 
it appears only in cases of heteromorphosis, but must be the result 
of some factor which is present only when heteromorphosis occurs. 
It is not then, properly speaking, a regional factor and therefore 
does not concern us at present; as a matter of fact it is undoubtedly 
a correlative effect, i. e., the presence or formation of oral struc- 
tures at the oral end of a piece retards the formation of similar 
structures at the aboral end of the same piece. : 
The experiments do not afford the slightest evidence for assuming 
the existence of a directive polar organization in the cesophageal 
region of Harenactis such as Driesch and certain others have pos- 
tulated, neither do they show any essential qualitative regional or 
axial differences in reaction; purely quantitative differences, 1. e., 
differences in the rapidity of reaction, are the only differences 
which appear, and it is probable that they constitute the only 
polarity which exists in this region: 
In the subcesophageal region, on the other hand, the two ends 
of the piece react differently, disc and tentacles appearing only at 
the oral end, while the aboral end redifferentiates more or less 
completely into the aboral structures removed. There can be no 
doubt that physiological differences exist at the two ends of the 
pieces in these cases, but such differences must be differences of 
correlation rather than of constitution, since any given level of the 
body in this region except the extreme aboral end gives rise to oral 
or aboral structures, according as it is in correlation with more 
proximal or more distal parts. Quantitative differences of con- 
