378 



RALPH S. LILLIE 



the beginning of divergences in the cleavage-rates of the blasto- 

 meres. For example, of eggs exposed at the time of the third 

 cleavage a considerable proportion (ca. 15 per cent) remained 

 uncytolyzed after fifteen minutes in the dilute sea-water; pre- 

 sumably these represent the more rapidly cleaving and the 

 more slowly cleaving fractions, which had either partly regained 



TABLE 2 



August 17, 1915. Arbacia eggs were fertilized at 11.05 a.m. From this fertilized 

 lot portio7is were transferred to dilute sea-water at the following times: (1) shortly 

 after fertilization (11.07 and 11.11), {2) midway between fertilization and cleavage 

 (11.29), (3) at a time when the cleavage furrow was first visible in a majority 

 of eggs (11.50), (4) and (5) after the completion of cleavage (12.00 and 12.08), 

 (6) at the beginning of the second cleavage (12.20), (7) ten minutes after the com- 

 pletion of the second cleavage (12.33), (8) at the beginning of the third cleavage 

 (12.48), and (9) ten minutes after the completion of the third cleavage (1.00). 

 Two dilutions of sea-water were used: (a) 60 volumes tap water plus 40 sea- 

 water, and (b) 65 tap water plus 35 sea-water. The second column gives the 

 condition of the eggs at three minutes and at fifteen minutes after placing in the 

 60 per cent dilute sea-water 



TIME OF PLACING IN DILUTE SEA-WATER AND 

 CONDITION OF EGGS AT THAT TIME 



EFFECT OP 60 PER CENT DILUTE SEA-WATER ON 

 EGGS (condition AFTER 3 AND 15 MIN- 

 UTES) 



11.07 and 11.11 (eggs with fertiliza- 

 tion membranes; otherwise un- 

 changed). 



11.29 (unchanged). 



11.50 (cleavage-furrow visible in 

 most eggs). 



12.00 (all in 2-cell stage). 



12.08 (all in 2-cell stage). 



12.20 (about one-third in early 4- 



cell). 

 12.33 (all in completed 4-cell stage 



12.48 (about one-third in early 8- 

 cell). 



1.00 (all in completed 8-cell stage). 



Eggs swollen, but intact. 



Eggs swollen, but intact. 



3 m. : ca. 20 cytolyzed; 15 m. : nearlj' 



all cytolyzed (ca. 90 per cent). 

 3 m. : practically all intact; 15 m. : 



great majority intact; ca. 10 per 



cent cytolyzed. 

 3 m.: practically all intact; 15 m. 



95 per cent or more intact; a few 



cytolyzed. 

 3 m. : ca. 50 per cent cytolyzed , 15 



m. : ca. 90 per cent cytolyzed. 

 3 m. : practically all intact; 15 m. : 



great majority (ca. 80 per cent) 



intact; remainder cytolyzed. 

 3 m.: ca. 30 to 40 per cent cytolyzed; 



15 m. : 80 to 90 per cent cytolyzed ; 



a fair proportion remain intact. 

 3 m.: nearly all intact; 15 m.: great 



majority' intact (ca. 75 to SO per 



cent); remainder cytolyzed. 



