SUSCEPTIBLE AND RESISTANT PHASES OF THE 



DIVIDING SEA-URCHIN EGG WHEN SUBJECTED 



TO VARIOUS CONCENTRATIONS OF LIPOID- 



SOLUBLE SUBSTANCES, ESPECIALLY 



THE HIGHER ALCOHOLS. 



FRANCIS MARSH BALDWIN. 



INTRODUCTION. 



That dividing Arbacia eggs show periods of varying suscep- 

 tibility and resistance when exposed to chemical substances 

 and to various physical conditions has been proved by numerous 

 investigations. When eggs, from a single fertilized lot were 

 placed at regular successive intervals after fertilization in cyanide- 

 containing sea-water (m/ioo to w/2Oo), Lyon' 2 found that they 

 were highly resistant to poisoning fifteen or twenty minutes after 

 fertilization, while eggs exposed to the same solution at the time 

 of cytoplasmic division were promptly killed. Later, after the 

 first division had been completed, the resistance to poisoning 

 again returned, followed by a second susceptible period at the 

 second cleavage. Loeb 3 later noted that the unfertilized eggs 

 show greater resistance to cyanide poisoning than the fertilized 

 eggs, and Mathews 4 indicated that in dividing eggs, the period 

 of maximum susceptibility is "immediately before and during 

 segmentation," and that just after segmentation the egg becomes 

 relatively highly resistant. Similar results were obtained by 

 Spaulding 5 in experiments with weak solutions of ether (1/64 

 per cent, in sea- water). The period of high resistance continued 

 up to the beginning of the first cleavage, and then fell during 

 cleavage to zero, with a sharp rise immediately afterwards. 

 There was a short period of susceptibility immediately following 



1 From the Marine Biological Laboratory, Woods Hole, Mass., and the Depart- 

 ment of Zoology, Iowa State College, Ames, Iowa. 



2 E. P. Lyon, Amer. Jour. Physiol., 1902, Vol. 7. p. 56. 



3 J. Loeb, Biochem. Zeitschr., 1906, Vol. i, p. 200. 



4 A. P. Mathews, BIOL. BULL., 1906, Vol. n, p. 137. 

 6 E. G. Spaulding, BIOL. BULL., 1904, Vol. 6, p. 224. 



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