Physiological Morphology 



93 



which it was directed in the normal condition. We may speak 



in such cases of polarization. The clearest example of this I 



foimd in an actinian, Cerianthus membranaceus. 

 If we cut a rectangular piece, cdef, out 



of the body-wall of Cerianthus new tentacles 



soon begin to grow out of this piece, but 



only from the side ef (Fig. 29), which was 



directed toward the oral end of the animal. 

 Nothing of the sort oc- 

 curs in the side c e, or 

 dc , OT fd. The produc- 

 tion of tentacles takes 

 place before any other 

 regeneration begins. 

 The same polarization is 

 shown in the following 

 variation of the preceding 

 experiment. If we make 

 an incision, a c6 (Fig. 30), 

 into the body-wall of the actinian, only the 

 lower lip, b c, produces tentacles, while the 

 upper lip, a c, produces none. The two 

 ends heal together in such a way that one- 

 half of a mouth, with its surroimding ten- 

 tacles, b (Fig. 31), is formed. It is curious 

 to see how these tentacles behave if we offer 

 them bits of meat. They endeavor to force 

 them into the new oral disc, where the 

 mouth should be, and only after a struggle 



of some minutes do they give up the futile attempt. I tried 



in every possible way to produce tentacles in the aboral end 



of a piece which had been cut out, but without success. 



Hydra behaves, as regards polarization, a little differently 



from Cerianthus. If we make an incision in the stem, a 



■A 



FiQ. 29. — Diagram- 

 matic. If a piece c d 

 e/ is cut out from tlie 

 wall of Cerianthus, a 

 sea anemone, new 

 tentacles are formed 

 only at the upper cut 

 ef. 



w 



Fig. 30. — Diagram- 

 matic. If an incision 

 a c 6 is made into the 

 body of Cerianthus 

 new tentacles grow 

 out only from the 

 lower edge c h. 



