A SIMPLE CASE OF SALT ANTAGONISM IN STARFISH 



EGGS. 



By RALPH S. LILLIE. 



{From the Marine Biological Laboratory, Woods Hole, and the Nela Research 

 Laboratories, Nela Park, Cleveland.) 



(Received for publication, April 23, 1921.) 



The freshly laid egg of the common starfish, Asterias forbesi, 

 is surrounded by a thin layer of water-swollen or gelatinous material, 

 of about 15 to 20 microns in diameter (one-eighth to one-twelfth 

 the egg diameter of about 160 microns), invisible to ordinary ob- 

 servation, but readily demonstrated by mounting the eggs in a some- 

 what thick suspension of India ink in sea water and examining on 

 a slide under a moderate magnification. Each egg then appears 

 surrounded by a clear halo outlining the space between the egg 

 surface and the outer limit of the jelly which is impermeable to the 

 ink particles. It is present in all full sized eggs, both mature and 

 immature, but is absent in the smaller ovarian eggs of two- thirds 

 or less the full diameter; evidently the water-swollen material of 

 which it consists is separated from the egg during the later period 

 of ovarian growth. In the starfish egg the jelly is remarkably re- 

 sistant to solution in ordinary sea water and is not removed by re- 

 peated washing in this medium, even with the aid of centrifuging; 

 in this respect the Asterias egg differs from the Arhacia egg which 

 is surrounded by a jelly otherwise similar but readily removed by 

 washing in sea water. In unfertilized starfish eggs the jelly shows 

 no change after 24 hours in sea water; but it gradually disappears 

 in fertilized cleaving eggs, possibly in consequence of increased 

 separation of CO2 from the eggs, since, as Garrey^ has shown, it 

 combines with acids and in so doing acquires increased swelling 

 properties. 



1 Carrey, W. E., Biol. Bull, 1919, xxxvii, 287. 



783 



