ON PHYSIOLOGICAL MORPHOLOGY. 



43 



II. POLARIZATION. 



While the foregoing experiments were in progress, I 

 observed that in many animals I was unable to produce 

 any kind of heteromorphism. These animals showed, in 

 regard to the formation of organs, a 

 phenomenon with which we are familiar in 

 a magnet. If we break a magnet into 

 pieces, every piece has its north pole on 

 that side which in the unbroken magnet 

 was directed toward the north. Likewise, 

 there are animals every piece 

 of which produces, at either 

 end, that organ toward which 

 it was directed in the normal 

 condition. We may speak in 

 such cases of polarization. 

 The clearest example of this 

 I found in an actinian, Ceri- 

 anthus membranaceus. 



a 



\\\\\|/// / / 



FIG. 9. 



c d 



FIG. 10. 



If we cut a rectangular piece, abed, out of the body- wall 

 of Cerianthus (Fig. 9), very soon new tentacles begin to grow 

 out of this piece, but only from the side 

 (Fig. 10), which was directed toward 

 the oral end of the animal. Nothing of 

 the sort occurs in the side, c d, or ac, 

 or bd. The production 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, 

 abc (Fig. 11), into the body-wall of the > 

 actinian, only the lower lip, be, produces 

 tentacles, while the upper lip, a c, pro- 

 duces none. The two ends heal together 

 in such a way that one-half of a mouth, 

 IG ' "' with its surrounding tentacles, a (Fig. 12), 

 is formed. It is curious to see how these tentacles behave if 



FIG. 12. 



