708 RALPH S. LILLIE 
TABLE 2 
August 22,1910. Eggs were exposed to0.65 m KCNS for & minutes, then returned 
to sea-water, and after the following intervals transferred to hypertonic sea- 
water in which they remained 30 minutes. The results were as follows: 
INTERVAL BEFORE 
NO. TRANSFER TO HYPER- RESULT 
TONIC SEA-WATER 
minutes 
tootsie Re ae 10 From one-half to two-thirds of the eggs form 
| larvae; many vigorous surface-swimmers 
Dee By Ae 20 Also shows a large proportion of active larvae 
though apparently fewer than in Experiment 
Bieter hee Pa kcm igs 30 Decidedly fewer larvae than in experiments 
1 and 2; about 5 per cent of the eggs form 
larvae; a good many surface-swimmers 
LARA aidan SPEYS 40 Still fewer eggs form larvae—ca. 1 per cent; 
a few surface-swimmers 
~ 
2 of table 2, though the proportion was still high.“ It is clear that 
during the period succeeding the return from the salt-solution to 
sea-water the egg undergoes a progressive series of changes of 
such a kind that the favorability of the response to the hypertonic 
sea-water undergoes decided decrease after the lapse of a certain 
interval, which, in these eggs, appears to be about fifteen or twenty 
minutes at normal summer temperature (20° to 22°). The nature 
of these changes can at present only be inferred; but if we accept 
the view proposed above that the effect of the hypertonic sea-water 
is to bring the permeability—which has been increased by the salt- 
solution—again toward normal, the conditions become partly 
intelligible on the assumption that the initial state of increased 
permeability cannot be prolonged beyond a certain period without 
14 Loeb’s experiments (with Moore: loc cit., pp. 78, 79) also show that too long 
an interval must not be allowed to elapse between membrane-formation and trans- 
fer to hypertonic sea-water. The time-relations in these experiments were, how- 
ever, decidedly different from the above. Eggs brought into hypertonic sea-water 
two hours after membrane-formation showed a high proportion of favorable 
development. The difference, I believe, is to be explained as due partly to the 
more resistant character of Strongylocentrotus eggs, and partly to the fact that 
the temperature of the sea-water in Loeb’s experiments was low (12°). The favor- 
able interval between membrane-formation and exposure to hypertonic sea-water 
would undoubtedly be several times shorter at a temperature 10° higher, as in my 
experiments described above. 
