672 STUDIES IN GENERAL PHYSIOLOGY 
whether it was possible for the unfertilized K eggs to reach 
the trochophore stage without any visible external signs of 
cleavage.’ I shall have to postpone a definite answer to 
this question until next year. 
Another point worth mentioning is the fact that phenomena 
‘of cleavage seem to be reversible in this form, inasmuch as 
an egg divides 
into two spheres 
which very soon 
fuse again. Such 
8.041 8051 changes, which 
occur very sud- 
denly, may be 
occasionally ob- 
served inunfertil- 
ized Cheetopterus 
8.05} 8.06} eggs. Fig. 159 
shows the succes- 
sive stages which 
were observed in 
one egg within 
er four minutes. I 
had watched these 
lively changes for several minutes before I decided to draw 
them. The egg had been for an hour in a mixture of 95 ¢.c. 
sea-water-+5 c.c. 24n NaCl,and had been back in sea-water for 
eight hours. When I began to draw the egg, it had the appear- 
ance of being in the two-cell stage (Fig. 159, 8:04). Ten 
seconds later it changed suddenly into a three-cell stage, the 
upper sphere breaking into two cells (8:044). A few seconds 
after this the lower sphere began to flow into the right upper 
sphere (8:05), and at 8:054 it had disappeared completely. 
The egg was again in the two-cell stage (8:05). Then the 
1 Professor F, Lillie in the following year confirmed this suggestion. [1903] 
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