THE DIVIDING SEA-URCHIN EGG 
299 
which are fairly comparable to those shown before; that is, they 
are typically reversible (see figure 52). 
SUMMARY 
1. The developing sea-urchin egg when subjected to suitable 
concentrations of various lipoid-soluble substances — i-amyl, hex- 
yl, 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 evi- 
dence 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 dif- 
ference could be detected by varying slightly the durations of 
exposure. Eggs exposed for five, eight or even ten minutes to 
the same concentration gave similar results. This, however, prob- 
ably would apply only within narrow limits. 
REFERENCES 
1. E. P. Lyon, Amer. Jour. Physiol., vol. 7, p. 56, 1902. 
2. J. Loeb, Boichem Zeitschr., vol. 1, p. 200, 1906. 
3. A. P. Mathews, Biol. Bull., vol. 11, p. 137, 1906. 
4. E. G. Spaulding, Biol. Bull., vol. 6, p. 224, 1904. 
