HETEROMORPHOSIS 159 



10. The morphogenetic polarity discussed in the preced- 

 ing chapter therefore corresponds with a polarity in regard 

 to the orientation of a Cerianthus toward gravitation. Since, 

 however, we are as little acquainted with the structural con- 

 ditions which determine the orientation of a Cerianthus as 

 with the structural conditions which determine that the for- 

 mation of tentacles only occurs at the oral end of a fragment, 

 the question as to whether the same conditions underlie both 

 phenomena cannot as yet be discussed. 



XII. FURTHER REMARKS ON THE FORM AND LIFE PHENOMENA 

 OF THE NEWLY FORMED HEADS IN CERIANTHUS 



1. If a transverse incision such as described in sec. x 

 be made fairly close to the head, the edges of the wound do 

 not draw together so easily. In this case new tentacles, a 

 new oral plate, and a new mouth are formed at the oral cut 

 edge. The part above the incision may persist for months, 

 but finally it drops off like a wilted leaf. 



If, on the other hand, the incision is made in the middle 

 of the animal, the tendency for the edges of the wound to 

 heal together is very great. New tentacles (external and 

 internal) and a new oral plate are formed; but never has a 

 mouth formed in any of the cases observed thus far. The 

 newly formed head was therefore of no use whatsoever to the 

 animal. If we look more closely at such a head (Fig. 24, &), 

 the ectoderm is seen to pass over into an oral plate at 6, 

 which is covered with two rows of tentacles. An opening no 

 longer exists in the ectoderm. 



We saw, moreover, that quadrangular pieces cut from the 

 wall of a Cerianthus formed tentacles upon one side only. 

 A second circumstance to be considered is the fact that the 

 elastic tension of the inner layer of the wall is greater than 

 that of the external. In consequence of this, the three 

 remaining cut edges, upon which no tentacles are formed, 



