Il8 FERTILIZATION 



eflPect polyspermy. There is an obvious conceptual fallacy in this 

 suggestion : the speed at which egg acid would have to be produced 

 to achieve the desired result would be so high as to make egg acid 

 production equivalent to a fast block to polyspermy. In the same 

 paper these workers make the startling suggestion that the develop- 

 ment of the hyaline layer plays a part in preventing polyspermy 

 in normal eggs. They do not comment on one consequence of this 

 suggestion: that if it is true, spermatozoa must be able to pass 

 through the fertilization membrane. Until someone sees this 

 occur, we need not consider whether a special mechanism (i.e. the 

 hyaline layer) exists to obviate any ill effects from its occurrence. 

 Intracortical and intracytoplasmic conduction. There has been 

 some discussion as to whether the cortical change (or the block to 

 polyspermy) is conducted round the cortex or through the cyto- 

 plasm. After comparing the form of the curve showing the rate at 

 which the sea-urchin egg surface becomes covered by the cortical 

 change with two 'models', in which this was eifected by intra- 

 cortical and intracytoplasmic diffusion of a substance with mole- 

 cular weight 20,000, I tentatively came to the conclusion (Roths- 

 child, 1949^) that if a diffusion mechanism was involved, the evi- 

 dence pointed towards the substance diffusing through the egg 

 cytoplasm and hitting various points on the cortex from the inside, 

 rather than towards diffusion in the cortex itself. Runnstrom & 

 Kriszat (1952) came to the opposite conclusion on the basis of 

 experiments done with damaged sea-urchin eggs. When these eggs 

 become stuck to a glass surface and are subsequently fertilized, the 

 part of the cortex which is stuck to the glass surface can be fer- 

 tilized independently of the rest of the egg, when the egg is un- 

 stuck. They concluded that the cortex was injured by being stuck 

 to the glass, that the cortical change was propagated round the 

 cortex and that consequently the injured part remained unfer- 

 tilized. The logical flaws in this argument are not difficult to see. 

 If part of the cortex is upset by being stuck to a glass surface, it 

 might be equally incapable of reacting to some stimulus from 

 within as from neighbouring uninjured parts of the cortex. In any 

 case, Horstadius & Runnstrom (1953) have recently described 

 experiments which might support the opposite viewpoint, in- 

 tracytoplasmic conduction; as, if an egg is constricted in a glass 

 tube so that it is nearly cylindrical in shape, and is fertilized at one 

 end, a fertilization membrane appears at both free ends but not in 



