HETEROMORPHOSIS 145 
When the roots were brought in touch with the surface 
of the water, the latter acted upon the root as a solid body. 
The root began to grow rapidly in length, attaching itself to 
the surface of the water (as if it were the surface of a solid 
body). Whenever a root adhered to a solid body new stems 
arose from that surface of the root which lay diametrically 
opposite to the solid body. Usually these branches then grew 
FIG. 24 FIG. 25 
perpendicularly away from the surface of the solid body. 
When new stems arose from roots growing along the surface 
of the water, the stems grew vertically downward. 
X. ON THE FORMATION OF TENTACLES IN CERIANTHUS 
MEMBRANACEUS 
1. I shall now discuss some experiments upon animals 
which seem to behave in accordance with Allman’s theory of 
polarity, inasmuch as in these I did not succeed in producing 
a head in the place of an aboral pole. The experiments 
led however to the production of several heads lying one 
above the other in one and the same animal (see Figs. 24, 
25). The irritability of the new heads could easily be com- 
pared with that of the old. In these experiments, more- 
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