MEMBRANE FORMATION IN FERTILIZATION. 89 



they had been in the sea watef for one hour or more, a more 

 normal membrane was formed and the eggs developed into plutei. 

 Why did the eggs only live to the blastula or gastrula stage when 

 they were fertilized immediately after the alkali treatment? 

 Should this have had something to do with the abnormal char- 

 acter of the membrane which was formed when the egg was fer- 

 tilized immediately after the alkali treatment? Were the cells 

 pressed by the membrane which was too tight, and did this 

 pressure kill them if prolonged? If this were the case, a tearing 

 of the membrane should save the life of the egg. It would be of 

 interest to try this experiment. 



3. In a recent number of the Comptes rendus de V Academie des 

 Sciences, Brachet has published an observation which may or 

 may not be similar to the one just mentioned. He found a year 

 ago that if the eggs of the sea urchin, Paracentrotus lividus, at 

 Roscoff , are put for two hours in contact with sperm of Sahellaria 

 alveolata (which cannot fertilize the eggs) and if they are after- 

 wards fertilized with sperm of their own species, they develop 

 without apparently forming a fertilization membrane. From 

 this Brachet concludes that the formation of a fertilization 

 membrane is not necessary for development, a conclusion which 

 will surprise nobody who is familiar with my first experiments on 

 artificial parthenogenesis, or who has ever fertilized eggs which 

 have been lying in sea water for several days. Moreover, Brachet 

 observed that the sea urchin eggs which are fertilized with sperm 

 of their own species, after two hours' treatment with the sperm of 

 Sahellaria, die at the time of gastrulation. The prolonged treat- 

 ment of the eggs of Paracentrotus with the sperm of Sahellaria 

 seems therefore to have a similar effect as the short treatment of 

 the egg of Strongylocentrotus with the alkaline NaCl solution in 

 my experiments. 



4. The deductions which Brachet draws seem, however, difficult 

 to reconcile with each other. We stated already that he assumes 

 that the eggs of Paracentrotus after two hours' treatment with 

 the sperm of Sahellaria form no fertilization membrane after 

 fertilization with their own sperm. Yet, he states further that 

 these eggs die in the gastrula stage for the reason that they cannot 

 hatch; for if he shakes the eggs and thereby destroys "la couche 



