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 ahvays 

 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 IRRITABILITY 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 



