PHASES OF DIVIDING SEA-URCHIN EGG. 139 



results with a five-minute exposure, when the exposure is pro- 

 longed to eight minutes, very little or no difference is detected. 

 This generalization, however, could probably be applied only 

 within narrow limits. 



The data from two experiments using capryl alcohol in 0.035 

 and 0.045 v l- P er cent, concentrations respectively are given in 

 Table V. These records are fairly typical of results of other 



experiments. 



SUMMARY. 



1. The developing sea-urchin egg when subjected to suitable 

 concentrations of various lipoid-soluble substances i-amyl, 

 hexyl, heptyl, octyl and capryl alcohols shows unmistakable 

 rhythms of susceptible and resistant phases, which when taken in 

 connection with the earlier observations of Lyon, Herlant, 

 Mathews, Spaulding, Lillie and others, constitute additional 

 evidence that a very intimate relation exists between the 

 general physiological condition of the egg, and the physical state 

 of its plasma-membrane. 



2. During the first ten or fifteen minutes after fertilization 

 the eggs are more susceptible than at any other time until the 

 period just preceding division. A comparatively resistant phase 

 gradually becomes more and more marked up to just before the 

 first cell-division (about 45 or 48 minutes after fertilization). 

 This is followed by a period of decidedly increased susceptibility 

 which lasts for about 15 or 20 minutes, during which time marked! 

 cytological effects are noted. Subsequently the resistant phase 

 is largely recovered, and maintained up to the time of the second 

 cleavage. 



3. The most favorable concentrations of the various alcohols 

 for demonstrating the rhythm of susceptibility range as follows: 

 i-amyl, between 0.7 and 0.9 vol. per cent.; hexyl, between 0.13 

 and 0.17 vol. per cent.; heptyl, between 0.06 and 0.07 vol. per 

 cent.; normal octyl, about 0.015; while capryl was considerably 

 above its isomere (normal octyl) between 0.035 and 0.045 vol. 

 per cent. The best records were obtained in experiments using 

 i-amyl and capryl alcohols, possibly indicating a higher specific 

 toxicity of these when compared to the others. 



4. When suitable concentrations were used, no marked 



