152 STUDIES IN GENERAL PHYSIOLOGY 
For the time being, therefore, the place where the ten- 
tacles in Cerianthus are formed is determined by the following 
law, which is only a somewhat modified expression of All- 
man’s theory of polarity: 
The place where the tentacles are formed on a fragment 
of Cerianthus is dependent upon the orientation which the 
Fragment had in the uninjured animal. The tentacles always 
grow upon the cut surface which was directed toward the 
oral pole of the uninjured animal. 
If for any reason, therefore, we might wish to know how 
a fragment of Cerianthus had been oriented in the uninjured 
animal, we should only have to wait until new tentacles were 
formed; the side upon which the tentacles sprouted would be 
that which was directed toward the head. 
XI. RELATIONS BETWEEN FORM AND JRRITABILITY IN 
CERIANTHUS 
As is well known, it is possible to determine from the 
physical behavior of a fragment of a crystal how it was 
oriented in the crystal. I have tried to determine whether 
or not relations between body form and irritability can be 
shown to exist in living animals comparable to those existing 
between the geometrical form and the physical behavior of 
crystals. Such a relation, indeed, exists in Cerianthus, and 
this can be recognized, not only in the uninjured animal, 
but also in the animal deprived of its head or foot. This is 
true, under certain conditions, even in fragments of an ani- 
mal. In this way it is sometimes possible to recognize from 
the behavior of a fragment toward external conditions which 
of its ends was originally directed toward the oral pole. 
When the external conditions permit of it, Cerianthus 
membranaceus assumes a position in which its long axis is 
absolutely or nearly vertical, and in which its oral pole is 
directed upward and its aboral pole downward. If the head 
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