122 STUDIES IN GENERAL PHYSIOLOGY 
Contrary to the theory of the “polarity” of the animal 
body, therefore, fragments of Tubularia mesembryanthemum 
are able to form polyps even at their aboral ends. 
2. I supported pieces cut from the stem of Tubularia 
mesembryanthemum in such a way that both cut ends were 
surrounded by water. To do this I sup- 
ported them in the meshes of a long wire 
net, or in the holes of a metal plate set up 
in the aquarium for this purpose. Polyps 
were formed at both the oral and the aboral 
ends of the fragments, so that the stem 
terminated in a head at each end. Fig. 
16 represents such an animal sketched from 
life and enlarged twice. ab is the piece 
removed from the old Tubularian. Polyps 
were formed at both ends, and the stem 
then grew in length from both ends. ac 
and bd are the new pieces that grew after 
the formation of the polyps. 
I have in this way been able to produce 
at any time any number of animals which 
terminate in an oral pole at each of the two 
ends of their body. I shall hereafter 
designate animals which terminate in a head 
at each end bioral animals. 
I would particularly emphasize the fact that such an 
animal remains bioral for the rest of its life. It is a 
well-known fact that in a normal animal the oral polyp is 
lost spontaneously after some time, and that a new one is 
formed sooner or later in its place. In the case of the bioral 
animals a constant blooming, shedding, and reappearance of 
the polyps occurs, not only at the oral end, but also at the 
aboral end, during the entire duration of their life. 
3. I was able, therefore, not only to cause the develop- 
"PIG. 16 
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