ORGANIZATION AND GROWTH 235 



tween growth and the amount of water in the solution was in 

 all points essentially the same as detailed here. We found in 

 a preceding chapter that the polyp is regenerated later in a 

 very highly concentrated or a very dilute solution than in a 

 solution the concentration of which lies between these two 

 extremes. We have therefore to determine in how far this 

 circumstance compels us to make corrections in the experi- 

 mental results given above. Between the concentrations 

 4.4-2.5 per cent, the difference in time between the forma- 

 tion of polyps in the different concentrations is so slight 

 that they need not be considered. So far as the very con- 

 centrated solutions, 5.1 and 4.6 per cent., are concerned, I 

 have made experiments which I have continued for weeks 

 and months, and have found that the absolute increase in 

 length during this time is practically zero, even though the 

 animals formed new polyps repeatedly during this time. 



4. I have not made any measurements on the increase in 

 the thickness of Tubularia. Yet the effect of the concen- 

 tration of the salt solution upon the diameter of the newly 

 formed stem was very apparent even without measurements. 

 The new stems formed in the more concentrated solutions. 

 Those in which about 1 g. of NaCl had been added to each 

 100 c.c. of sea-water were markedly thinner than the old ones 

 which had been grown in ordinary sea- water. On the other 

 hand, in the diluted sea-water the thickness of the new stems 

 was not only not less than that of the old stems, but even 

 greater. 



5. With an increase in the concentration of a salt solu- 

 tion the amount of oxygen dissolved in it decreases, and, as 

 we shall see later that this is an important factor in regenera- 

 tion and growth, we must determine whether differences in 

 concentration influence the growth of Tubularia through their 

 effect upon the amount of oxygen dissolved in the solutions 

 and, if so, how much. The one direct measurement of the 



