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 



