THE MATURE EGG, UNFERTILIZED AND FERTILIZED 79 



d. Size, Weight and Density of Egg 



10 c. mm. eggs, dry wt. 2.63 mg. (Krahl, 1950) 

 10 c. mm. eggs, wet wt. 10.9 mg. 



Dry weight is approximately 24% of wet weight (Krahl, 1950). 



1. 08 1 to 1.087; same to 16 cell stage; blastula lighter than 16 cell stage, but heavier 



than sea water; plutei 1.055 to 1.066 (Lyon, 1907). 

 1.0485 to 1.0656, unfertilized (Heilbrunn, 1926a, 1928, p. 71). 

 1.090, unfertilized, with jelly (E. N. Harvey, 1931, 1932 a). 

 1 .084, unfertilized, without jelly. 



e. Size of Fertilized Egg 



It is generally accepted that the fertilized egg (without fertilization 

 membrane) is the same size as the unfertilized (Whitaker, 1933 b), 

 though it is larger by the addition of the hyaline layer, which is extra- 

 neous to the egg proper (E. B. Harvey, 1933 a for A. lixula). But Glaser 

 (1913; 1914a, b, c; 1924) found the tgg smaller by 2.5 \j. immediately 

 after fertilization, then larger, and also R. S. LilUe (1916a) smaller by 

 i.o [J.. Chambers (1921 a) found it slightly larger, and Shapiro (1948b) 

 found an increase of 2.7% in volume. There is no appreciable increase 

 in diameter until the gut is complete in the gastrula stage, about 17 

 hours after fertilization (E. B. Harvey, 1949). 



f. Variation in Size 



Average size of unfertilized egg as recorded by some investigators is 

 shown in the following tabulation. The figures in brackets are computed 

 from the figure given by the author. 



