160 SruDIES IN GENERAL 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 isa 
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 
FIG. 35 
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. Ifa 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; 
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