672 



STUDIES IN GENEKAL PHYSIOLOGY 



8.04 



8042 



805 



8.05J 



whether it was possible for the unfertilized K eggs to reach 

 the trochophore stage without any visible external signs of 

 cleavage. 1 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 

 changes, which 

 occur very sud- 

 denly, may be 

 occasionally ob- 

 served inunfertil- 

 ized Chsetopterus 

 8.05i 806 806|- 808 eggs. Fig. 159 



shows the succes- 

 sive stages which 

 were observed in 

 one egg within 

 four minutes. I 

 had watched thef e 



lively changes for several minutes before I decided to draw 

 them. The egg had been for an hour in a mixture of 95 c.c. 

 sea-water + 5 c.c. 2i|nNaCl, 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 8:05^ 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] 



FIG. 159 



