tion. 10. Clear quarter, about 32 cells, and white halt photographed at 

 the same time, further advanced, 5 hours after fertiHzation. 11. Early 

 blastulae of clear quarter and white half from the same culture, about 

 6/2 hours after fertilization. 12. Free-swimming blastula of clear quar- 

 ter, 20 hours after fertilization. 13. Pluteus of clear quarter, 10 days old. 



Photographs 14 to 17. Eggs centrifuged after fertilization. 

 Photograph 14. Eggs centrifuged one minute after fertilization for six 

 minutes at 10,000 x g; they break up into small pieces. 15. Egg cen- 

 trifuged four minutes after fertilization for six minutes at 10,000 X g; 

 it stratifies like the unfertilized eggs, but not nearly so well (Cf. with 

 Plate VII, Photograph 1). 16. Egg broken apart by centrifuging for 

 six minutes, thirty minutes after fertilization, the fertilization mem- 

 brane having been removed previously; picture was taken 2/2 hours 

 after fertilization. Note that the white half has cleaved, and red half 

 has not. 17. Eggs form long streamers when centrifuged 6 to 20 min- 

 utes after fertilization, the membranes having been removed just after 

 fertilization. This photograph was taken while the eggs were rotating 

 (about 6,000 X g). (Photographs 1-13 J. Exp. Zool. 102:269, 1946a.) 



PLATE XIII. 



Stratification of unfertilized eggs and size of half -eggs with varying 

 centrifugal forces. The first vertical column shows stratification. The 

 second vertical column shows size of half -eggs. With low forces, the 

 eggs are well stratified and the white half is much larger than the red 

 half. With high forces, the eggs are not well stratified and the white 

 half is small while the red half is very large. Photograph 5. Red half 

 obtained with 10,000 X g and recentrifuged at 10,000 X g. Control to 

 Photograph 12; note clear layer at top, due to further settling of gran- 

 ules. Photograph 12. Red half obtained with 100,000 X g and recentri- 

 fuged at 10,000 X g. The granules had not been segregated in the first 

 centrifuging with very high forces, and when recentrifuged, they 

 stratify as in the original egg. The mitochondrial layer has been 

 stained with methyl green. (Biol. Bull. 80:357, 1941a.) 



PLATE XIV. 



Stratification of unfertilized eggs and size of half-eggs when centri- 

 fuged in hypo- and hypertonic sea water ( 10,000 X g ) . Magnification 

 about 270 X . In hypotonic sea water ( Photographs 1 to 3 in 60% and 

 4 to 6 in 80%), the clear layer is large, with few granules; the heavy 

 granules are well packed as compared with control eggs in sea water 

 (Photographs 7 to 9). The white half-eggs (Photographs 2 and 5) are 



