160 STUDIES IN GENEKAL PHYSIOLOGY 



roll inward, so that only the ectoderm is visible externally 

 (Fig. 35). Because of these mechanical conditions the part 

 assumes after some time especially when the new tentacles 

 begin to grow an appearance which reminds one in some 

 ways of a normal Cerianthus. Of course, many pieces remain 

 permanently monstrosities. So far as the experi- 

 ments performed hitherto are concerned, a mouth 

 has never been formed in these pieces. This is a 

 remarkable fact, and seems to indicate that the 

 animals have a source of food-supply which 

 differs from that of the uninjured animal, for they remain 

 alive, and do not diminish markedly in bulk even in the 

 course of months. 



2. These mouthless heads when brought in contact with 

 food reacted exactly as normal heads. The reader is prob- 

 ably acquainted from personal observation with the behavior 

 of an Actinian when a piece of meat is laid upon the tip of 

 one of its tentacles. The tentacle becomes concave toward 

 the piece of meat, winds itself about the meat as a vine 

 about a support and finally bends so that the piece of meat 

 reaches the middle of the oral plate, where the mouth is 

 situated in normal animals. In Cerianthus the inner ten- 

 tacles then fold over the meat; some or all of the external 

 tentacles then follow in a similar way, and it looks as though 

 the tentacles were pressing the meat into the mouth. The 

 meat reaches the stomach, and the tentacles then unfold. 

 But this reaction is certain to occur only when the sub- 

 stance laid upon the tentacles has certain chemical and 

 mechanical characteristics. If a grain of sand is laid upon 

 the tentacles instead of the meat, the tentacles do not bend 

 in as described. 



If a piece of meat is carefully laid upon the tip of the 

 external tentacles of a newly formed head, which has no 

 oral opening, they also seize it in the manner just described; 



