226 E. G. SPAULDING. 



the event of cleavage. To the first two possibilities correspond 

 the effect respectively of lack of oxygen and the use of strongly 

 hypertonic solutions on the fertilized egg ; to the second method 

 our own results with ether, HC1, etc. From this hypothesis it 

 can also be reasonably inferred that the nearer to the point of 

 termination of the preparatory process that either method is used, 

 so much the less will its effect in general be, and this supposition 

 is again confirmed by experimental results. 



Lyon l found that the effect of KCN on the fertilized Arbacia 

 egg, taking, c. g., various strengths of a titrated solution mixed 

 with sea water, was the indication of " successive stages of 

 relatively high and low resistance in each cleavage." Putting 

 the eggs into the solution at successive five-minute periods after 

 fertilization and allowing them to remain perhaps one hour, then 

 washing and removing to sea water, he found that "there is a 

 stage about ten or fifteen minutes after fertilization when the egg 

 is especially susceptible to KNC." " Again soon offer the first 

 cleavage comes a second stage of small resistance ; a third fol- 

 lows the second division." " The resistance of the egg to KNC 

 increases up to a maximum up to the time of separation into the 

 two cells." " The effect of KNC is the same as lack of oxygen." 



In interpretation of these results Lyon says that the processes 

 dependent upon oxygen seem to begin about 1015 minutes 

 after fertilization, for if they are inhibited the egg does not seg- 

 ment and they recur at each segmentation. To identify them 

 with the morphological processes of the splitting and separation 

 of the chromosomes or with the dissolution of the nuclear mem- 

 brane seems to him to be impossible, for these occur too late to be 

 directly affected. Wilson and Matthews, 2 he says, mention how- 

 ever two processes which occur sufficiently near to the suscep- 

 tible stage to be worthy of consideration in this respect. One is 

 the growth and division of the sperm aster, the other the growth 

 of the nucleus. From the part which in order to explain the 

 constricted form of cleavage 3 must be attributed to, as played by 

 each of these processes, the supposition that they are affected by 

 a lack of oxygen, by KCN, etc., receives confirmatory evidence. 



1 Lo;. cit. 



' 2 Journal of Morphology, 1895, X., p. 319. 



;! Lillie, R. S., BIOLOGICAL BULLETIN, IV., March, 1903; and Am. Jour, of 

 / v 'r.*/'i'/(;;'T, VIII., 4, Jan. 1903. 



