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 SKA-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 



