ON EGGS OF MARINE ANIMALS 51 



Acid in sea-water 



Of the various acids, mineral and organic, employed as means 

 for calling forth development to at least the larval stage, butyric 

 acid is most used. The work on Thalasse?na ought be noted, 

 but I can not comment upon it because of lack of experience with 

 this egg. I limit myself to the egg of Asterias. Carbon dioxide 

 is as eiTective as butyric acid. I suggest therefore that the 

 worker who has in mind an investigation on the effect of acid in 

 calling forth complete development, use the carbon dioxide 

 method as prescribed by Delage for the egg of Asterias glacialis, 

 or the butyric acid method as employed by R. S. Lillie on the 

 e^^ of A. forbesii or A. vulgaris. 



Double treatment 



By double treatment I mean the effect of two diflferent 

 means, each of which calls forth a different response from the 

 egg. Thus I do not include the action of two treatments with 

 butyric acid on the egg of the starfish or that of butyric acid 

 followed by heat, as used by R. S. Lillie. True double treat- 

 ment is that as used by Delage in his tannin-ammonia method 

 for the echinid egg, or that employed by Loeb. The Loeb 

 method is the more common. This is as follows: 



Uninseminated eggs are placed in 50 cc. of sea-water plus 

 2 cc. of N/io butyric acid for one and one-half to three minutes, 

 and removed to normal sea-water. Ten to fifteen minutes later 

 the eggs are removed from' sea-water to 50 cc. of sea-water plus 

 8 cc. of 2.^M NaCl. From this hypertonic sea-water they are 

 returned to normal sea-water at intervals between seventeen and 

 one-half and twenty-five minutes. 



Heilbrunn (1915) modified Loeb's method by taking 2.8 cc. 

 of N/10 butyric acid, instead of 2 cc, added to 50 cc. of sea- 

 water, which was allowed to act for 30 seconds. With this 

 method, he obtained 90 per cent, separated membranes in the 

 egg of Arbacia instead of the gelatinous films described by Loeb. 



For the egg of Echinarachnius (Just, 1919), I use 2 cc. 

 N/io butyric acid plus 50 cc. of sea-water acting for 35 seconds. 

 The subsequent residence in sea-water and treatment with the 

 hypertonic sea-water are as for the egg of Arbacia. 



