//. SEPARATION OF COMPONENTS OF 

 A, PUNCTULATA EGGS (AFTER HARVEY) 



The eggs of the sea urchin, Arbacia punctulata, have been em- 

 ployed particularly for cytophysical and cytochemical investiga- 

 tions. Therefore, it may be well to include here a short description 

 of the procedure developed by Harvey (1932, 1936) for the separa- 

 tion of components of this cell, especially since similar treatment has 

 been applied to the ova of other marine invertebrates and to other 

 cells employed for laboratory study. 



Centrifugation is carried out in tubes, a little larger than hema- 

 tocrit tubes, having a capacity of 0.7 ml. Place the eggs in 1 vol. 

 sea water over a layer of 2 vol. 0.95 M sucrose soln. (95% of 342 g. 

 sucrose added to 1 1. tap water) in the centrifuge tube. Roll the tube 

 gently to effect partial mixing. Centrifuge the eggs in this medium, 

 which is isosmotic and isopycnotic with the eggs, for 3-4 min. with 

 a centrifugal force of 10,000 times gravity. Three layers form with 

 the white halves above, under them a pinkish layer of elongated 

 whole eggs, and on the bottom the red halves. With more sucrose 

 solution, further centrifugation results in breaking of the halves 

 into quarters, as indicated in the diagram in Figure 159. 



452 



