462 



CHARLOTTE HAYWOOD. 



TABLE IV. 



EQUATIONS FOR THE RETARDATION OF 50 PER CENT. CLEAVAGE IN Arbacia 

 EGGS IN SEA WATER 30 PER CENT. TO " 100- '' PER CENT. SATURATED 



WITH CO 2 . 



(A preliminary experiment which showed a slope of 1.7 has been omitted 

 from the average since this value differs widely from those subsequently 

 obtained.) 



The numerical value 1.18 of the slope of the lines in Fig. 

 3 shows that the retardation in cleavage produced by a given ex- 

 posure is nearly, though not exactly, equal to the time of exposure. 

 A value of unity would indicate exact equality. The fact that the 

 slopes of the various lines are nearly the same is an indication of 

 the general similarity, already mentioned, of the CO 2 effects at all 

 tensions above 30 per cent, of saturation. The different values 

 of the intercepts are without significance in this connection, since 

 they represent merely the normal time of cleavage in those eggs 

 which were not exposed to carbon dioxide. 



SUMMARY. 



1. The first cleavage of the fertilized eggs of Arbacia is en- 

 tirely suppressed, or practically so, in the presence of amounts of 

 carbon dioxide greater than those corresponding to a 40 per cent, 

 saturation of sea water or a tension of approximately 300 mm. 

 Hg. In the presence of smaller amounts of carbon dioxide cleav- 

 age is possible, but is greatly delayed. 



2. Since a very considerable oxygen deficiency causes only a 

 slight delay in the cleavage process, the factor of oxygen lack is 

 probably a negligible one in the results here described. 



3. The effects of a complete suppression of the cleavage process 



