406 OTTO GLASER. 



receptors" (527). In other words, the egg is not always fer- 

 tilized, because there are obstacles or resistances. When these 

 are removed, fertilization, parthenogenesis, or auto-partheno- 

 genesis may occur. 



No circumstance connected with the initiation of development 

 that is not a common occurrence in all cases is capable of ex- 

 plaining how these obstacles or resistances can be removed. It 

 is not necessary for clear thinking on this subject to know what 

 they are at present, but the only common fact which seems capable 

 of explaining how these natural blocks to fertilization, and the 

 initiation of development could be removed, is at present the 

 increase in the permeability of the ovum. For this reason, with- 

 out in any way trying to minimize the significance of the facts 

 emphasized by the fertilizin theory, I believe that the permea- 

 bility change plays a very real part in the process of fertilization, 

 for through it is possible a disturbance of the equilibrium in 

 which we know the egg finds itself prior to impregnation or 

 parthenogenetic initiation. 



If this viewpoint is correct, the following picture of both 

 fertilization and parthenogenesis is possible. Fertilizin alone in 

 sufficient concentrations is capable of increasing the permeability 

 of the ovum; smaller quantities when activated by union with 

 sperm are able to exert the same effect. This alteration of the 

 surface may also be brought about by electricity, heat, cold, 

 mechanical shock, specific chemical alteration of the membrane, 

 lipoid solvents, pricking, or any other way of rendering the egg 

 surface more permeable or of accomplishing the same result as 

 an increase in permeability. The immediate effect of this per- 

 meability increase is a removal of those obstacles or resistances 

 which constitute the normal fertilization block. These removed, 

 the fertilizin within the egg combines with the egg-receptors, 

 but if fertilizin activated by sperm is present, the egg receptors 

 would combine with the elements for which ex hypothese they 

 have the greater affinity. 



So far the facts seem to group themselves harmoniously, but 

 how are we to conceive of the "obstacles" or "resistances"? 

 We might imagine the existence within the unfertilized egg of a 

 body capable of playing the required role, but for this assumption 



