EFFECT OF LACK OF OXYGEN. 153 



favorable, normal larvae are produced after readmission of oxygen 

 no matter at what stage in mitosis the eggs are subjected to 

 lack of oxygen. 



It might be of interest to compare briefly the results on oxygen 

 consumption of the sea urchin eggs with my results on lack of 

 oxygen. Warburg ('15) found that 10 minutes after fertilization, 

 the oxygen consumption in Strongylocentrotus was six times that 

 of the unfertilized egg and in the sixth hour was twelve times. 

 Shearer ('22) by means of a special type of Barcroft manometer 

 found that the oxygen consumption of Echinus eggs was eighty 

 times as great during the first minute after fertilization as 

 during the minute just before fertilization. The tremendous 

 increase in oxygen consumption occurs at the time that the 

 sperm comes in contact with the egg, before entrance. My 

 experiments have not included this early stage owing to difficulties 

 in technique. But it is interesting that Shearer obtained no 

 special increase in oxygen consumption at the time of the union 

 of the pronuclei, a stage which I found unaffected by lack of 

 oxygen, whereas he did obtain an increase at the time of first 

 cleavage (45-50 min. after fertilization), this corresponding 

 roughly to the period just before first cleavage in my experiments 

 when the effect of lack of oxygen was most pronounced (there 

 being a very short time interval between anaphase and cleavage). 

 Of course the period when most oxygen is consumed need not 

 necessarily be the period when the lack of oxygen is most felt, but 

 it is of interest that the two seem to harmonize to some extent. 



The peculiar cleavage figures following readmission of oxygen 

 to cells deprived of it during the metaphase are somewhat 

 similar to those obtained by Wilson ('oi) after recovery from 

 ether, though much more pronounced. Just what is the meaning 

 of the irregular cleavage, it is difficult to say, except perhaps 

 that it is a readjustment after a very profound disturbance 

 to the dividing cell due to lack of oxygen. There is no doubt 

 that very extensive changes can be made in the early cleavages 

 without affecting later development, as has been previously 



shown in many ways. 



SUMMARY. 



i. Observations were made on the living eggs of Echinus 

 microtuberculatus and Strongylocentrotus lividus in a hanging drop 



