116 STUDIES IN GENERAL PHYSIOLOGY 
it is possible so to change the form of the animal that it ter- 
minates at both ends either in oral (Fig. 17) or aboral poles, 
and yet continues to live. On the other hand, I have found 
animals in which all attempts at the transformation of organs 
have thus far been unsuccessful. To this group belong 
Cerianthus membranaceus and many other Actinians. I 
succeeded, however, in bringing about a permanent change 
of form in one of these animals (Cerianthus membranaceus), 
in which I was able to cause the growth of any number 
(within certain limits) of mouths, one above the other, in one 
and the same animal. 
The regeneration of lost organs in animals has often been 
made the subject of study, usually, however, only to see 
which organs can be regenerated, and further to study more 
closely the anatomical or histological details of the process 
of regeneration. But it has rarely been considered that 
these phenomena can give us an insight into the conditions 
that control the morphogenesis of animals. Where this has 
been done, it has almost always been with the intention of 
showing that under all conditions only one and the same 
organ grows from any definite point on the animal. 
Allman" was perhaps the first to define this sharply asa 
law of the formation of organs. From the well-known 
experiments of Trembley,’ Dalyell,* and from his own obser- 
vations, he formulated the theory of the “polarity” of the 
animal body. Allman cut pieces from the stem of Tubu- 
larians and marked the end which had been directed toward 
the head of the animal. Even though this cut end was mor- 
phologically entirely similar to the other, yet a head was 
formed only at this oral end, while no head was formed at 
1GrorcE J. ALLMAN, Report of the British Association for the Advancement 
of Science, 1864. 
2A, TREMBLEY, Mémoires pour servir d Uhistoire dun genre de polypes d'eau 
douce 4 bras en forme de cones (Leide, 1744). 
3J.G. DALYELL, Rare and Remarkable Animals of Scotland (London, 1847). 
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