ON EGGS OF MARINE ANIMALS 47 



rated membranes in order to determine which exposure gives the 

 highest per cent, of separated membranes. Repeat the experi- 

 ment removing the eggs now at 5 second intervals beginning 

 10 seconds before the stage that proved to be best in the first 

 series of experiments, and continue 10 seconds beyond. Inspect 

 the eggs again and choose that exposure which is optimum. 



Methods for Inducing Membrane-separation in 

 Unfertilized Eggs of the Genus Asterias 



Methods for caUing forth membrane-separation in eggs of 

 Asterias glacialis, A. vulgaris and A. forbesii comprise the use 

 of carbon dioxide, high temperature and butyric acid. The first 

 we owe to Delage (1902^, b and c)- R. S. Lillie (1908, 1916) 

 especially has used the second and third. With any one of these 

 methods, it is essential to use eggs whose germinal vesicles have 

 disrupted. 



Membrane-separation may be induced by means of carbon 

 dioxide either by exposing the eggs to sea-water charged with it, 

 or by crowding the eggs in sea-water. For the former a con- 

 venient apparatus is the ordinary syphon used for charging 

 water, the so-called sparklet bottle, as employed by Delage. 

 One fills the bottle to the red mark with clean sea-water and 

 charges it with the gas from the steel cartridge. The eggs are 

 flooded with the CO2 charged sea-water and removed at 10 

 second intervals. In this wise, the optimum length of exposure 

 is learned. Another set of eggs is treated with the charged 

 sea-water and the eggs removed at intervals around the optimum 

 exposure as previously determined in order more exactly to fix 

 the optimum exposure. This method is nicer than that of 

 crowding the eggs in a small quantity of sea-water. 



For the method of using butyric acid in sea-water for calling 

 forth membrane-separation in the egg of the starfish as well as 

 for that by means of heat, the worker may consult the original 

 papers by R. S. Lillie. 



Methods for Inducing Experimental Parthenogenesis 



The worker who wishes extensive treatment of the subject of 

 experimental parthenogenesis has available reviews, as those by 



