274 RALPH S. LILLIE. 



in experiments at other temperatures; in all cases the exposure 

 which induced the largest proportion of regular cleavages was 

 found to correspond with that at which the largest proportion 

 of eggs formed larvae. In the series of Table V. the optimum, 

 6 minutes, is somewhat shorter than usual; on June 24 the 

 optimum of cleavage was found at 7 minutes, and on June 26 

 at 8 minutes, with 10 minutes somewhat less favorable. 



Table V. 



June 25. 32°. 



Condition of Eggs 4 Hours after Exposure, and Proportion 

 Time of Exposure. of Eggs forming Larvae. 



1. 2 m Great majority are unchanged; a few have membranes. 



No larvae. 



2. 3 m Most eggs have typical membranes and are irregular 



or amoeboid in form; a few show irregular cleavages. 

 No larvae. 



3. 4 m Almost all eggs have membranes and exhibit irregular 



forms; a few have cleaved symmetrically. Ca. 

 5 per cent, form larvae. 



4. 5 m Marked improvement over Experiment 3: most eggs 



have cleaved, and many are in regular 4- and 8-cell 

 stages. Ca. 50 per cent, form larvae. 



5. 6m Almost all eggs are cleaved; cleavages are more regular 



and advanced than in Exp. 4; i6-cell stages are 

 frequent. 80-90 per cent, form larvae. 



6. 7 m The proportion of regular cleavages is also high, but 



rather less than in Exp. 5. Ca. 60 per cent, form 

 larvae. 



7. 8 m Cleavages are fewer and less advanced than in Exp. 6. 



Ca. 25—30 per cent, form larvae. 



8. 10 m Great majority are uncleaved; many are irregular in 



form or fragmented. Larvae are few: < 5 per cent. 



9. 12 m Almost none have cleaved. The eggs are largely 



irregular or with small surface-vesicles detached. 



While an exposure just long enough for membrane-formation 

 is insufficient by itself to induce normal cleavage and develop- 

 ment, it is possible, after forming membranes in this way, to 

 make the eggs cleave and develop to larval stages by subjecting 

 them to a second treatment with warm sea-water, or by after- 

 treatment with fatty acid (w/260 butyric acid in sea- water), 

 hypertonic sea- water, or cyanide («/iooo KCN in sea-water). 

 These effects will later be described in detail (c/. Tables XIIL, 

 XVII.). 



