RHYTHMICAL SUSCEPTIBILITY OF SEA URCHfN EGGS. 257 



Table II. 



T° = 19° — 21°. Hypertonic exposure =25 minutes. 



Time in normal sea 



water after acid 



treatment 5 15 25 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 no 



Blastulae per cent. ... - 5 16 23 30 11 9 10 12 9 5 6 7 9 13 16 12 5 4 

 Time in normal sea 



water after acid 



treatment 115 120 125 130 140 150 165 175 185 



Blastulae per cent. ... 812 8 4 o<i o i o 



It seemed possible that the normally fertilized eggs also might 

 show a rhythmical susceptibility to hypertonic sea water. 

 Especially did this seem probable in view of Lyon's experiments. 

 He found that normally fertilized eggs of Arhacia gave alter- 

 nating maxima and minima of susceptibility to heat, cold and 

 lack of oxygen; and that CO2 production was greatest at the 

 time of cytoplasmic division.^ E. G. Spaulding has shown a 

 rhythmical susceptibility and immunity of fertilized Arhacia 

 eggs to the effects of ether, HCl, KCl and NaCl. He found a 

 rise in immunity up to the time segmentation begins, followed 

 by a sharp decrease during cleavage, with a marked rise at the 

 end of cleavage.^ A. P. Mathews found an approximate rhyth- 

 micity in the behavior of Asterias eggs toward KCN solutions.^ 



In my own experiments the Arhacia eggs were fertilized in 

 one finger bowl and at the end of each ten-minute interval a lot 

 was removed to the hypertonic solution and kept there for 40 

 minutes, after which the eggs were returned to normal sea water 

 to develop. The results of a number of such experiments indi- 

 cate (Table III., Curve II.) that the maximal susceptibility 

 occurs just after fertilization (5-15 minutes) and immediately 

 before and during each cytoplasmic division, and that the maxi- 

 mal resistance is shown 35-45 minutes after fertilization and 

 just after each division. This corresponds to Lyon's statement 

 regarding the effects of heat upon dividing eggs, viz., that 

 Arhacia eggs are especially sensitive to heat just before division 

 and that they are most resistant after division. 



1 E. P. Lyon, Am. Journ. Physiol., Vol. 7, p. 56, and Vol. 11, p. 52. 



2 E. G. Spaulding, Biol. Bull., Vol. 6, p. 224. 

 ^ A. P. Mathews, Biol. Bull., Vol. 11, p. 137. 



