4O HARRIETT M. ALLYN. 



tempted was with KC1, and that did not result favorably for the 

 production of segmented swimmers. 



The method used was to suspend small flasks of sea-water in a 

 water bath whose temperature could be varied, and when the 

 temperature within the flask was at, or a little above, the desired 

 temperature, introduce the eggs. The eggs were thus suddenly 

 subjected to a rise of temperature of several degrees. The 

 apparatus, which was a crude one, did not keep the eggs at an 

 exactly even temperature, and the results will be given in each 

 case as the effect of a temperature within the limits of variation; 

 e. ., the most favorable temperature used was one which varied 

 between 32.5 and 34.5 C. The various temperatures tried 

 ranged from 30 C. to 47 C. From 35 C. up no swimmers were 

 produced, although there was some possible cleavage. 30 C. 

 induced almost no development. The eggs were left in the flask 

 for times varying from 35 seconds to 2 hours and 9 minutes, and 

 then removed to dishes on the table, where the temperature was 

 about 23-24 C. Other eggs were left in the flasks over night 

 to cool down slowly after the end of the experiment. It is 

 possible that in the very beginning of the experiment the tem- 

 perature was lowered a little by the introduction of the small 

 amount of water necessarily carried in with the eggs. The 

 optimum length of exposure to the heat was 40 minutes or near 

 it. The very brief exposures were made only for the high 

 temperatures. Less than 25 minutes for the lower temperatures 

 was ineffective in producing segmented swimmers, although 

 shorter exposures than that might show some polar body forma- 

 tion and a small amount of cleavage. 



The eggs did not usually extrude the first polar body until 

 removed from the warm water to the cooler, but then went on 

 promptly with one or both maturation divisions. The per- 

 centage forming both polar bodies was in general smaller than 

 that forming the first only. In the series of which I have sections 

 the second polar body was not seen to form at all, and only a few 

 eggs formed the first polar body. The series of fixed eggs is not at 

 all complete, as I expected to be able to make other series later. 

 The sections indicate that there is sometimes formation and 

 retention of the nucleus of the first polar body within the egg, for 



