HETEROMORPHOSIS 171 
the reverse phenomenon—namely, that the animal would 
leave the ulva leaf or the mussel shell to attach itself to the 
glass—occurred but rarely. This contact-irritability of the 
foot does not change when the head or the larger portion of 
the oral part of the animal is amputated. I kept the oral 
end of such a piece of an animal in contact with the bottom 
of the aquarium, while its foot extended upward. A slide 
was placed in contact with the foot, to which the animal 
might easily have attached itself, but this it did not do. As 
soon, however, as an ulva leaf floating in the aquarium came 
in contact with the foot, the animal attached itself to it 
immediately. 
7. The aboral pieces of transversely divided Actinia 
which still had a foot remained alive longer than the oral 
pieces. The latter usually succumbed to a fungus disease 
after a few weeks. The disease began ordinarily in the ten- 
tacles which had lost their turgidity after the operation. 
Contarini seems to have made a similar observation in opera- 
tions on Actinia (Aiptasia) diaphena. 
XVI. SUMMARY OF RESULTS 
In conclusion I wish to summarize briefly the chief results 
of these investigations. 
I. We saw first of all that there are certain animals in 
which it is possible to control the place where an organ is 
formed by external conditions, in such a way as to substitute 
in place of a lost organ one which differs from it in form and 
function (heteromorphosis). It is thus possible to produce 
at will forms with normal vitality, which differ from the 
hereditary forms produced by nature in a definite way. In 
detail the heteromorphoses thus far accomplished are the 
following: 
1. In Tubularia mesembryanthemum: 
a) If a piece of stem, which must not be below a certain 
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