222 STUDIES IN GENERAL PHYSIOLOGY 
their correctness. The growth of the new ganglion is fairly 
rapid. Instead of one large ganglion, several small ones 
were formed. For these reasons I have not followed further 
the question as to whether Ciona is at all heliotropic. Dr. 
P. Mingazzini has also observed the regeneration of the 
brain of Ciona after its removal; he suggests that the new 
ganglion is formed from the ectoderm, as in the embryo. 
VIII. THE RELATION BETWEEN REGENERATION AND THE 
CONCENTRATION OF THE SEA-WATER IN TUBULARIA 
1. Now that we have seen that it is possible to alter the 
inherited form of an animal by substituting one organ for 
another, we shall pass to experiments on the general physi- 
ological factors which underlie regeneration and growth in 
animals. These experiments, as the preceding ones, had to 
be made with the simplest experimental accessories, and in 
addition they were not completed when I was compelled to 
leave Naples. Since they can be continued only at the sea- 
shore, I shall here give only those experiments which have 
been carried to a certain degree of completion. 
If the polyp of a Tubularian is amputated, a new polyp 
regenerates. What general physiological conditions must 
be fulfilled in order that this may occur? Since the stem 
begins to grow as soon as the polyp is formed, the second 
question arises: What conditions influence growth? The 
following experiments are intended to answer these ques- 
tions. 
I shall first show how the absorption of water affects 
regeneration. The reader will know that from the point of 
view gained by a study of osmosis, the living protoplasm of 
plant cells is characterized by its permeability to water and 
its total or partial impermeability to many substances dis- 
solved in the water. There is no reason for believing that 
animal protoplasm behaves any differently in this respect 
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