THE PHYSIOLOGY OF FERTILIZATION 153 



cytoplasm to mechanical shocks (e.g., shaking) has been 

 similarly noted in the sea urchin egg by several investi- 

 gators. 



Such changes have recently been more carefully 

 investigated by Heilbrunn (1915) and by Chambers 

 (1917). Heilbrunn tested the viscosity of the proto- 

 plasm of the egg of the sea urchin by the use of the 

 centrifuge, and found that the separation of protoplasmic 

 granules of different specific gravity by centrifugal force is 

 much more readily effected before than after fertilization. 

 The protoplasm is much more fluid before than after 

 fertilization, and this can mean only a tendency toward 

 gelation in a colloidal system such as protoplasm; this 

 change was observed to begin two and one-half minutes 

 after insemination. Heilbrunn also determined that a 

 variety of parthenogenetic agents, and he believes all such 

 agents, produce a similar gelation effect, and he was 

 therefore led to regard the coagulation change as the 

 primary event in activation of the egg. 



Chambers investigated this subject by means of the 

 micro-dissection method as part of a study of the cell 

 aster which he interprets as a reversible gelation phe- 

 nomenon. When the sperm aster appears in the egg 

 of Echinarachnius about three minutes after penetra- 

 tion of the spermatozoon, it can be shown to be a more 

 rigid area by the fact that it can be pushed and rolled 

 in the surrounding more liquid cytoplasm by the micro- 

 dissecting needle. As the aster increases in size the 

 gelation effect extends. Chambers thus localizes the 

 gelation due to fertilization in the sperm aster, though 

 Heilbrunn's results appear to indicate a more general 

 effect; there is, however, nothing in Chamber's result 



