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 0, 
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, 
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