THE DIVIDING SEA-URCHIN EGG 
293 
McoKol. 
nor OF The cuft.ve of susteprisic HtsisT/w phases of thc 
m VI ©I NO S6A-HXCHSN ifeOS -^EW SuajEcTED TO 0-9 Vot. i-4M^ 
AWtoHOU Fo(\ tioHT lAiNi/TcS AT SuttSSWE Tin/ Mlf/iH’i, IhfTeaVAU. 
tions of 0.1, 0.25 and 0.30 vol. per cent respectively were used. 
The time of exposure was shortened to five minutes, for the reason 
that it was thought the concentrations were, if anything, a little 
above the optimum. The results clearly showed that the solution 
of 0.1 vol. per cent was not sufficiently toxic tO' demonstrate any 
variation of susceptibility in the eggs, since at whatever period 
they were exposed practically all eggs survived to the free- 
swimming blastula stage. On the other hand, the two higher con- 
centrations proved too toxic, so that practically none of the eggs 
continued their development after subjection to these solutions at 
any period. The 0.25 vol. per cent solution, although it suppressed 
further development, was not quite intense enough in its action to 
cause cytolysis in the eggs, with few exceptions. The 0.30 vol. 
per cent concentration caused very slight cytolysis, and rupture 
was almost universal. Accordingly, series of experiments were 
carried out to test the various concentrations between 0.1 vol. 
per cent and 0.25 vol. per cent. 
These results show a much less definite evidence of a rhythm of 
