206 STUDIES IN GENERAL PHYSIOLOGY 
edef is cut from the body of an Actinian, tentacles are 
formed upon only one of the four cut edges, namely, upon 
the oral surface ef. From this and similar experiments— 
which may be read in the original—it follows that the place 
where the new tentacles are formed in a fragment of Cerian- 
thus is determined by the orientation which 
the fragment had in the intact animal; just as 
a@ in every fragment of a broken magnet the 
position of the poles is determined by the 
orientation of the piece in the unbroken 
magnet. From this analogy—which, how- 
ever, goes no further—the term “polarity” 
has recently been applied to the organization of 
such animals. According to this idea, Cerian- 
thus would be a typical ‘‘polarized animal.” 
Now, Cerianthus is not a satisfactory sub- 
ject for investigation of the causes of “polar- 
ity ;” Tubularia mesembryanthemum, a Hydroid, adapts itself 
much better to these experiments.’ Tubularia ends in a root 
at its aboral end, and in a polyp at its oral end. If a piece 
is cut from the stem, and both cut ends are surrounded by 
water, a heteromorphosis results, as [ have shown in a former 
paper. A polyp arises from both cut ends, and a bioral animal 
is obtained. Yet the formation of polyps is different at the 
two ends in one particular: it is always more rapid at the 
oral than at the aboral pole. In so far as this fact renders 
it possible to determine which was the oral and which the 
aboral end in the uninjured stem, it can still be considered 
as an expression of polarity. The following experiments 
deal with the internal conditions which determine the differ- 
ence in time between the formation of the polyps at the oral 
and at the aboral ends in Tubularia. 
The starting-point of these experiments is J. Sachs’s 
b- 
FIG, 52 
1See Part I, p. 115. 
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