Physiological Morphology 



93 



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

 in such cases of polarization. Thr ohvirest example of this I 

 found in an actinian, Ceriatithus membranacem. 



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), whicli was 

 directed toward the oral end of the animal. 



Nothing of the sort oc- 

 curs in the side ce, or 

 dc , or 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, acb (Fig. 30), 

 into the body-wall of the actinian. only the 

 lower lip, be, 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 surrounding ten- 

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

 to see how these tentacles behave if we offer 

 them bits of meat. Thev endeavor to forei' 

 them into the new oral disc, where the 

 mouth should l)e, and only after a struggle 

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

 in every possible way to proiluce tentacles in tlie al)()ral end 

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



Hydra behaves, as regards i)olarization. a little differently 

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



Fio. 29.— DiaKram- 

 matic. If a pli-cr r d 

 ef Is cut out from the 

 wall of Cenanthun. a 

 si'a aiu'inoiu". iM've 

 tt'iUacli's ar»' fornird 

 only at till' upiHTCut 

 ef. 



yj 



Fig. 30. — Diagram- 

 matic. If an incision 

 a cb is made into the 

 body of Cerianthus 

 new tentacles grow 

 out only from the 

 lower edge c h. 



