290 RALPH S. LILLIE. 



For comparison eggs were exposed to 32° without previous membrane-formation 

 for 4, 5, 6, 7, 8, and 10 minutes; the optimum exposure was 8 minutes at which 

 50-60 per cent, of the mature eggs formed larvae. A sperm-fertilized control also 

 yielded numerous larvae. 



After-exposure to 32° for the proper time thus greatly increases 

 the proportion of favorably developing eggs. No marked im- 

 provement is seen until the duration of after-exposure reaches 

 four minutes; with longer exposures the proportion of eggs 

 forming larvae shows progressive increase up to an optimum at 

 about seven minutes; a decline then follows; an exposure of 10 

 minutes effects only slight improvement, and one of 12 minutes 

 appears ineffective. Similar results, differing slightly in detail 

 in different series, were obtained in eight other series of experi- 

 ments. In general, after the preliminary membrane-formation 

 by one minute's exposure to n/260 butyric acid, the time of 

 exposure to 32° required for optimal development was found to 

 range from 5 to 7 minutes; one minute's exposure to n/260 

 butyric acid appears thus physiologically equivalent to warming 

 at 32° for the same or a somewhat longer period. After-treat- 



Table XV. 



M/260 Butyric Acid with After-treatment with Sea-water at 34°. 



August 27. The eggs from one starfish were used. The eggs were few in 

 number, but the majority showed normal behavior. They were exposed to w/260 

 butyric acid for one minute and then returned to sea-water. Later (within 20 

 minutes) portions were exposed to hypertonic sea-water, cyanide, and warm sea- 

 water as indicated. 



After-treatment. Results. 



1. None (control) Typical membrane-formation, followed by breakdown 



of almost all eggs. One blastula found. 



2. Hypertonic sea water 



for 30 m 35-45 per cent, of the eggs form larvae. 



3. w/iooo KCN for 30m. . .Ca. 50 per cent, of all eggs form larvae. 



4. 34° for I min Only a few eggs form larvae: < i per cent. 



5. 34° for 2 min Marked improvement: 20-30 per cent, form larvae. 



6. 34° for 3 min Larvae are fewer than in Exp. 5: ca. 20 per cent. 



7. 34° for 4 min Few eggs form larvae: < i per cent. 



8. 34° for 5 min Most eggs fail to divide; none form larvae. 



Warming at 34° without previous membrane-formation: Eggs were exposed to 34** 



in the usual manner for 2, 3, 4, 5, 6, and 7 minutes. The best development resulted 

 from the 2- and 3-minute exposures, with respectively 25-35 per cent, and 35-40 

 per cent, of eggs forming larvae; with the 5-minute exposure only 5 per cent, formed 

 larvae. 



