102 



FERTILIZATION 



consistency of the cortex may not be unequivocal, in the sense of 

 being able to separate cortical from cytoplasmic changes. Table i6 

 is of interest in several different fields of cell physiology. First, it 

 presents biological evidence of structural and, probably, metabolic 

 changes in the cortex, induced by activation ; secondly, it provides 

 a number of clues for the further investigation of the cortex; and 



Permeability 

 Hypotonic s.w. 

 Salts 



Strong bases 



Ammonia 



Strong acids 

 Fatty acids 

 Ether 

 ALcotiol 

 Cloroform 

 Chloral Hydrate 

 Acetone 

 Saponin 



Digitonin ...^^_____^_^^___________^^ 



Zbmin. ^75min,,, 



Fertilization Amphiaster 



Metaphase 



Cleavage ends 



FIG. 19. — Changes in the susceptibility of the sea-urchin egg to various reagents. 

 Each horizontal section shows the percentage cytolysis at different times 

 after fertilization. The hatched regions at the top are periods of high 

 permeability. After Herlant (1920). 



thirdly, the information may not only apply to the fertilized egg, 

 but to other dividing cells. Now that we understand a little more 

 about cell membranes and, with the aid of labelled atoms, can in- 

 vestigate sodium, potassium, phosphorus and, perhaps, calcium 

 fluxes across the cell surface, more rapid progress should be 

 possible in this field, in spite of the complications introduced by 

 the possibility of active transport. Among other things, it would 

 be interesting to examine the effects, if any, of saponin and digi- 

 tonin on the form and intrinsic birefringence of the cortex, in the 

 ways described by Mitchison & Swann (1952). 



