Factors III Regeneration 345 



Polyps were produced in all the jars. The greatest number 

 appeared in the control dish No. i. The previous experiment 

 showed that no polyps are produced in water from which the oxy- 

 gen had been removed. But in this experiment the water reab- 

 sorbed enough oxygen from the overlying layer of air to supply 

 the needs of the developing polyps. Where large quantities of 

 oxygen had been removed from sea-water as in Nos. 4, 5, 6 

 and 7 a much longer time was required to absorb enough oxygen 

 to permit regeneration to begin; and the available supply of 

 oxygen w^as more quickly exhausted in these than in Nos. 2 

 and 3, therefore, regeneration ceased earlier in the former series 

 than in the latter. It follows that ivhere much oxygen has been 

 removed from sea-water, polyps appear later and disappear earlier 

 than on stems kept in ivater containing more oxygen. 



EFFECTS OF DIRECT SUNLIGHT-" 



Experiment 2j. This experiment unfortunately was not carried 

 to completion. The apparatus was so placed that the sun shone 

 directly upon the stems for about eight hours daily. The heat 

 of the sun was guarded against by reducing radiation from the 

 table and fixtures to a minimum and by surrounding the dishes 

 by large volumes of water to which ice was sometimes added. 

 Temperature records of each of the dishes were made at least 

 three times daily. The stems were grouped as follows : 



1 Dish was not guarded against the heat ot the sun. 



2 Dish was surrounded by 3000 cc. of water. 



3 Dish was surrounded by 9000 cc. of water. 



I, 2 and 3 were exposed to the direct rays of the sun. 



4 Not exposed to the light, but kept in the shade ot the room. 



5 Not exposed to the light, but kept in a dark chamber. 

 The temperature in i was, of course, several degrees higher 



than in any of the other dishes, especially about midday, when 

 the temperature was often as high as 28° C. In 2, the tempera- 

 ture was lower, while in 3, 4 and 5, which were practically the 

 same, the temperature was lowest. 



^'Loeb '92, '96; Driesch Zool. Jahrb. '90; Goldfarb '06. 



