ACTIVATION OF UNFERTILIZED STARFISH EGGS. 283 



warm sea-water (32°) ; in all five, however, the optimum lay- 

 between five and ten minutes.^ There is thus an approximate 

 constancy in the time of exposure required to induce complete 

 development with solutions of this concentration. Probably 



Table XII. 



iV/260 Butyric Acid. 



Condition of Eggs 4 Hours after Treatment, and Proportion 

 Time of Exposure. forming Larva;. 



1 m All eggs have membranes; most are irregular or 



amoeboid in form; none are cleaved. No larvae. 



2 m Similar to i m. lot, but a few eggs {ca. 2-3 per cent.) 



are in the 2-celI stage. No larvae. 



3 m Generally similar to the 2 m. lot, but the cleavages 



are inore numerous {ca. 10-15 per cent.), mostly 

 2-cell with a few 4-cell stages. Very few larvae 

 (< I per cent.). 



4 m Cleavages are more numerous and advanced; 40-50 



per cent, are cleaved, mostly 2 and 4-cell, with a 

 few 8-cell stages. Larvae still few {ca. i per cent.). 



5 m Cleavage is more advanced than in the 4 m. lot; ca. 



50 per cent, are cleaved, largely 8- and i6-cell 

 stages. Ca. 10 per cent, form larvae. 



6 m Most eggs are cleaved {ca. 70-80 per cent.), many in 



16- to32-cell stages. Ca. 50 per cent, form larvae. 



7 m Almost all eggs are cleaved (90 per cent, or more), 



many in normal-looking 16- to 3 2-cell stages. 

 70-80 per cent, form larvae. 



8 m Similar to 7 m. lot; most eggs are in 16- to 32-cell 



stages. 65-75 per cent, form larvae. 

 10 m Cleavages are fewer and less advanced; ca. 70-75 



per cent, are cleaved, mostly 4- and 8-cell stages. 



65-75 per cent, form larvae. 

 12 m Comparatively few cells are cleaved; ca. 10 per cent. 



are in 2- or 4-cell stages, largely irregular; the rest 



uncleaved. 25-35 per cent, form larvae. 

 15 m Almost all eggs remain uncleaved, and many show the 



beginnings of surface-disintegration. Few form 



larvae, — ca. i per cent. 

 Controls: Unfertilized eggs disintegrate without membrane-formation or de- 

 velopment. Nearly all sperm-fertilized eggs develop to larvae. 



1 This variability may be due partly to the fact that on account of the lateness 

 of the season and consequent scarcity of ripe starfish the eggs used in these experi- 

 ments came from fewer animals; thus in Series i, 4, and 5, eggs from only one star- 

 fish were used in each case, and in Series 2 and 3 from three. In the earlier experi- 

 ments with warm sea-water the mixed eggs from several animals were used in 

 each series. 



