PHASES OF DIVIDING SEA-URCHIN EGG. 



129 



zation) and above this concentration the toxicity is such that 

 the decline in survivals is very rapid. In 1.25 vol. per cent, 

 solutions, all eggs are killed in all stages with exposures of nine 

 minutes. 



Table I. summarizes the results of a typical series of experi- 

 ments with i-amyl alcohol. This particular series of experiments 

 was started in the afternoon of July 16, and the observations 

 noted in the third column were carried over into the morning of 



TABLE I. 



I-AMYL ALCOHOL. 



July 16, 1:45 P.M. The fertilized eggs were placed at the intervals after 

 fertilization noted in column i in 50 cc. of 0.9 vol. per cent i-amyl alcohol. Al 

 exposures except the first (i) (6 minutes) were of eight minutes duration. 



Intervals After 

 Fertilization. 



Observed Condition of the Eggs at the 

 Time of Removal from Sol. 



Proportion Forming Blastulse and Con- 

 dition of Remaining Eggs Next Day. 



(1) 3- 9 m. 



(2) 10-18 m. 



(3) 20-28 m. 



(4) 30-38 m. 



(5) 40-48 m. 



(6) 50-58 m. 



(7) 60-68 m. 



(8) 70-78 m. 



(9) 80-88 m. 



Fertilization-membranes well 

 formed. No marked cytolytic 

 change noted. 



No marked change in appearance. 

 Uniform. 



Membranes markedly swollen in 

 some cases. Slight fading of 

 pigment. 



A few cells plasmolyzed, other 

 membranes markedly swollen. 



No marked change. Faint indi- 

 cation of cleavage furrow in a 

 few scattered cells. 



About 65 per cent, have entered 

 the two-celled stage. Some 

 show shrinkage. 



About 90 per cent, in two-celled 

 stage. Others intact. 



Practically all in two-celled stage. 



A few are starting second cleav- 

 age furrow. 



About 5 per cent, form free 

 swimming blastulae. Consider- 

 able numbers cytolyzed. 



About 10 per cent, form blastulae. 



Not so badly cytolyzed; most 

 cells intact. 



Nearly 30 per cent, free-swim- 

 ming blastulae. Most eggs 

 intact. 



Between 30 and 40 per cent, 

 free-swimming blastulae. Most 

 others intact but swollen. 



Large majority (75-80 per cent.) 

 form swimming blastulae. 



Relatively few (less than 10 per 

 cent.) form surviving blastulae. 



Between 30-35 per cent, form 



blastulae. 

 Few (15-20 per cent.) form 



blastulae. Others intact. 

 3-5 per cent, form blastulae. 



Others intact. 



the following day. A similar series of experiments performed at 

 about the same time with the same alcohol in somewhat lower 

 concentration (0.8 vol. per cent.), but with slightly longer 

 (lo-minute) exposures yielded substantially the same results. 

 On the following day experiments were carried out on eggs 

 subjected to i.i vol. per cent, solutions with only brief (3-, 4- 

 and 5-minute) exposures with the results noted above. 



