Factors III Regeneration 349 



In the experiments of 1905 the total number of polyps was daily 

 recorded. These records agree with those of Loeb, that the num- 

 ber regenerated increases with the increased dilution of sea-water. 

 The maximum regeneration is reached in sea-water diluted 15 

 to 20 per cent; beyond this point, that is, in solutions more 

 diluted, regeneration rapidly decreases; in 40 per cent, few polyps 

 are produced, in 50 per cent, none. 



In 1906 the experiment was repeated, but the records indicate 

 the number of different hydranths daily regenerated. The results 

 are practically in accord with the data obtained by the other 

 method in 1905. The rate of development in both series was the 

 same in normal sea-water and in solutions diluted as much as 15 

 per cent but beyond this point the greater the dilution the greater 

 the retardation. 



Stems of Pennaria tiarella behave in quite the same manner as 

 Eudendrium in dilute solutions of sea-water. The results in both 

 hydroids are practically the same. 



Experiment 2g. An effort was made to acclimatize the stems 

 of Eudendrium and Pennaria to greatly diluted sea-water, and 

 thereby to have them regenerate in solutions diluted 50 per cent 

 or more. Sea-water was daily diluted 2h per cent more than the 

 preceding day. Polyps appeared in all dilutions until 45 per 

 cent was reached, beyond which regeneration ceased on Euden- 

 dridm stems, while Pennaria 'ceased at 50 per cent. In the very 

 diluted solutions polyps were distinctly smaller than the normal 

 polyps. The experiment seemed to show thathydranths of Euden- 

 drium and Pennaria could not be made to regenerate in solutions 

 diluted more than 45 and 50 per cent, respectively, during the 25 

 days of the experiment. 



