370 EALPH S. LILLIE 



indicated, however, that the period of maximum suseeptibihty 

 is 'immediately before and during segmentation," and that just 

 after segmentation the egg becomes relatively highly resistant. 

 This conclusion was supported by observations of Spaulding^ 

 on the variations of resistance to weak solutions of ether (eV 

 per cent in sea-water), which gave an unusually clear result; 

 the resistance proved high (with the exception of the period 

 immediately following fertilization) "up to either just before 

 or the beginning of the first cleavage; during the early part of 

 cleavage it falls to zero, with a sharp rise afterwards and a fall 

 at the second segmentation" (p. 232). Spaulding also found a 

 similar though less definitely marked variation of susceptibility 

 to acid and salt-solutions (pure isotonic KCl and NaCl). A 

 rhythmical variation in the physiological state of the cell is 

 thus associated with the rhythm of the cell-division process. 

 This variation involves changes in both the metabolism and 

 the physical condition. Lyon^ showed that the eggs were most 

 readily injured by heat (e.g., 35° for 5 minutes) at the time of 

 division, and recovered resistance after cleavage was complete; 

 he also made the important observation that the evolution of 

 CO 2 follows a parallel course, reaching a maximum at the time 

 of cleavage. This indicates a rhythm of oxidation-processes; 

 and the resistance to lack of oxygen (hydrogen atmosphere) 

 appears to follow a similar rhythm. More recently Conklin*^ 

 has described results of a related kind in experiments on Cre- 

 pidula eggs; various abnormal conditions (warm sea-water, 

 dilute and concentrated sea-water, ether, strong electrical cur- 

 rents) produce abnormalities (of cleavage, distribution of chro- 

 mosomes, etc.) in these eggs; "the greatest changes are produced 

 when the eggs are in some phase of kinesis at the beginning 

 of the experiments, while stages of interkinesis are affected rela- 

 tively little;" in general, "eggs are much more susceptible to 

 injury during division than during rest."^ Similarly A. R. Moore 



^ E. G. Spaulding, Biol. Bull., 1904, vol. 6, p. 224. 

 * Lyon, Amer. Journ. Physiol., 1904, vol. 11, p. 52. 



« E. G. Conklin, Journ. Acad. Nat. Sc. Philadelphia, 1912, vol. 15, 2nd ser., 

 p. 503. 



"> Loc. cit., pp. 525, 538. 



