l82 L. V. HEILBRUNN. 



drop is then covered by a coverslip with a drop of sperm sus- 

 pension on its lower surface, and to the other drop is added a 

 drop of the same sperm suspension, but no coverslip, a marked 

 difference between the two preparations can be noted. In 

 the absence of a coverslip, a much greater per cent, of eggs 

 undergo membrane elevation. When the drop of sperm sus- 

 pension is added to the eggs after the coverslip has been placed 

 in position, practically no membrane elevation occurs. In 

 these experiments, the coverslip was always supported by strips 

 of paper or thin glass tubes, so that there could be no question 

 of compressing the eggs. 



The effect of the coverslip is in part due to the action of the 

 glass (or of substances diffusing out of it) 1 on the spermatozoa. 

 The sperm apparently congregate at the surface of the coverslip. 

 But this is not believed to be the only effect, and some evidence 

 that I possess, although not absolutely unimpeachable, tends to 

 show that the pressure of the coverslip is also partly responsible 

 for preventing elevation. However, further experiments on 

 this point are necessary; I merely bring up the matter here in 

 order to emphasize the difficulties in the way of direct obser- 

 vation. Fol ('79) speaks of the great difficulty in observing 

 fertilization in the sea-urchin egg. Pictet ('91) found no such 

 difficulty, but I think that the cortical effect that he describes 

 was not membrane elevation, but membrane swelling, which 

 is not retarded by the presence of the coverslip. 2 



My observations, though admittedly incomplete, tend to show 

 that the membrane is elevated from all sides of the egg at the 

 same moment. It is possible that elevation does start at the 

 point of sperm entrance as Ries ('09) for example claims, but 

 if this part of the membrane does show any priority, it is only 

 an exceedingly brief one. 



On the basis of Loeb's view that the sperm contains a lysin 

 which produces membrane "formation" directly, we would have 

 to suppose that this lysin diffuses around the egg surface in 

 incredibly fast time. The morphology of sperm membrane 

 elevation offers a severe obstacle to most theories which attempt 



1 Possibly dissolved out by the alkali of sea-water. 



2 Both Pictet and Fol subjected the eggs to slight compression. 



