458 CHARLOTTE HAYWOOD. 



cleaved eggs, a few ciliated larvae have been found to develop 

 after an exposure of two and one half hours, and the first cleavage 

 has made its appearance in 95 per cent, to 100 per cent, of the 

 eggs subjected to very nearly 100 per cent. CO 2 for this length of 

 time, though relatively few normal larvae were obtainable after 

 such long exposures. In one experiment that illustrated in 

 Table III. exposure of the eggs to 80 per cent. CO 2 for over ten 

 hours still permitted reversibility of the cleavage process to the 

 extent that, six hours after the eggs had been returned to sea 

 water, 88 per cent, were found to have divided, although develop- 

 ment was very abnormal and went no farther than the first few 

 cleavage stages. Apparently the process of nuclear division is 

 an extremely powerful one and, as has been observed by others, 

 can persist even when the cell itself is unable to divide. 



Fig. 2 is a typical illustration of the series of cleavage curves 

 which are obtained with various lengths of exposure to a rela- 

 tively high tension of carbon dioxide. It will be observed that 

 the first cleavage ultimately occurs in practically all of the eggs, 

 even after prolonged exposures. The relation of the exposure 

 time to the total retardation is a matter of some importance in in- 

 dicating the nature of the observed effects. If the narcosis pro- 

 duced by carbon dioxide were complete and were followed by in- 

 stantaneous recovery the resulting retardation of cleavage, as com- 

 pared with normal controls, should be exactly equal to the time 

 of exposure. Incomplete narcosis, on the other hand, would tend 

 to shorten, and a more gradual recovery, to lengthen, the period 

 of retardation. Theoretically, a combination of these two effects 

 might conceivably, under a given set of conditions, result in a net 

 retardation exactly equal to the period of the exposure, but it is 

 believed that such a balancing of effects could not account for the 

 results about to be described. Since with all tensions above ap- 

 proximately 30 per cent, saturation the relation of time of expo- 

 sure to total retardation is essentially the same, it is difficult to 

 imagine that the CO 2 tension should, above this point, either be 

 without effect on a measurable rate of development or that a de- 

 crease in this rate should always be followed by a correspondingly 

 increased rate of recovery. The reasonable interpretation of the 



