292 RALPH S. LILLIE. 



produced by this form of after-treatment, whether the membrane- 

 formation is induced by heat or by fatty acid; in either case 

 warming for a few minutes completes the process of activation 

 and enables the eggs to develop favorably. Precisely the same 

 effect is gained by after-exposing eggs, in which membranes 

 have been formed by either method, to weak solutions of fatty 

 acid for a brief period; the effects of such treatment are in all 

 respects similar to those of after-warming. This is illustrated 

 by the following experiment (Table XVI.). 



It is clear that in the time-relations of its action as well as in 

 its other characteristics, this form of after-treatment resembles 

 closely that with warm sea-water. It is also possible to treat 

 the eggs first with warm sea-water and then after-treat with 

 butyric acid solution; precisely the same results follow as in 

 the experiment just described. This is illustrated by the following 

 series (Table XVII.). 



Table XVII. 



Brief Exposure to 32° with After-treatment by w/260 Butyric Acid. 



September 7. The eggs from one starfish were used; eggs were few but appar- 

 ently normal, over 90 per cent, showing normal maturation, and sperm-fertilization 

 resulting in a large proportion of larvae. The eggs were exposed to sea-water at 32° 

 for 3 minutes, then returned to sea-water at normal temperature, and 16 minutes 

 later placed in n/260 butyric acid solution, from which they were again returned 

 to sea-water after the times indicated. 



After-treatment. Results. 



1. None (32° for 3 m. 



alone) No development; only a small proportion form mem- 

 branes. 



2. JV/260 butyric acid: 



2m All form membranes but few are cleaved after three 



hours. Ca. 5 per cent, form larvae. 



3. Butyric acid: 4 m A large proportion (50-60 per cent.) are cleaved after 



three hours. More than 50 per cent, form larvae. 



4. Butyric acid: 6 m Most eggs are cleaved after three hours. 70-80 per 



cent, form larvae. 



5. Butyric acid: 8 m In contrast to Exp. 4, few eggs are cleaved after three 



hours, and only 1-2 per cent, form larvae. 



6. Butyric acid: 10 m No eggs cleave within three hours. None form larvae. 



The favorable effect of this after-treatment is evident. It 

 will be noted that the three minutes' exposure to 32° was in- 

 sufficient for membrane-formation in most eggs; but the effect 



