HETEROMORPHOSIS 173 
b) It was possible to cause the growth of roots in the 
middle of a stem by bringing this point in contact with 
solid bodies. 
5a) It was possible to grow tips from the basal cut end of 
a stem of Sertularia polyzonia by fixing the stems in the 
aquarium with their basal ends upward (toward the source 
of light). New roots were usually formed at this end in 
addition to the new tips (Fig. 22, a, b). 
b) So far as my present experiments go, new branches 
were formed only on that side of the old stem or root which 
was turned toward the light. 
6. It was possible to produce biapical animals in Gono- 
thyre Lovenii. 
II. In a long series of animals, particularly Actinians, I 
have not yet succeeded in causing a heteromorphosis of any 
kind. In these animals the position of the regenerated 
organ is determined (as far as our present knowledge goes) 
by the orientation of the fragment occupied in the uninjured 
organism, a new head is formed at the oral edge of a piece 
of such an animal, while a new foot is regenerated at the 
aboral end. This law governs regeneration, not only in 
Actinia, but also in Hydra, in certain starfish which I have 
studied, in a series of worms, snails, crustaceans, and animals 
still higher in the scale. 
III. The same behavior in organization is therefore found 
in the animal kingdom as in the vegetable. As is well 
known, it is possible to control the position of a new organ 
(just as in the animals given under heading I) in certain 
plants, while in others (as in Actinians) regeneration is 
dependent upon conditions which are at present unknown, 
and are apparently internal. 
IV. The following are mentioned as some of the different 
forms of irritability which influence the orientation of animal 
organs : 
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