454 CHARLOTTE HAYWOOD. 



of course, be readily found by interpolation from the cleavage 

 curve. 



RESULTS. 



Before discussing the typical effects of carbon dioxide, it is 

 necessary to rule out the possibility that oxygen lack might be a 

 contributing factor in the results produced, since the method used 

 in saturating the sea water with carbon dioxide causes at the same 

 time a removal of oxygen. Although a complete lack of oxygen 

 has been shown to stop the cleavage process in sea urchin eggs 

 (E. B. Harvey, 1927), the present work indicates that even with 

 an extensive reduction in oxygen tension cleavage is able to con- 

 tinue and at a rate but little slower than normal. The results of 

 the thirty minute exposures to low tensions of this gas, represent- 

 ing but 14 per cent, to 18 per cent, of those available for the con- 

 trols, are given in Table I. and show that the cleavage time under 

 these conditions was delayed but a few minutes. 



TABLE I. 



THE EFFECT UPON CLEAVAGE OF THIRTY MINUTE EXPOSURES TO Low 



OXYGEN TENSIONS. 



cc. of Oxygen Minutes Required for 



Solution. per Liter. 50 per cent. Cleavage. 



Sea water 5.6 60.5 



Nitrogen-saturated sea water 0.76 68.5 



Sea water 5.48 62.5 



Nitrogen-saturated sea water 0.97 64.2 



A direct comparison of the effects of low oxygen tension and of 

 high carbon dioxide tension has been made in another experiment, 

 in which each of four portions of egg suspension was exposed for 

 thirty minutes to one of the following solutions : 



cc. of Oxygen 

 pH. per Liter. 



1. Sea water 5.15 



2. Sea water + oxygen +CO (60% saturated)... 5.3 5.56 



3. Sea water + nitrogen -f- CO 2 (60% saturated) 5.3 1.26 



4. Sea water, saturated with nitrogen 0.55 



It will be evident that solutions 3 and 4 were low in oxygen as 

 compared with solutions I and 2, while solutions 2 and 3 were high 



