152 PROBLEMS OF FERTILIZATION 



Summarizing this section we have the following 

 evidences of increase of permeability of the plasma 

 membrane at the time of fertilization: increase of 

 oxygen consumption, escape of substances from the egg 

 at the time of fertilization (increased CO 2 , pigment, 

 jelly in Nereis, etc.), decrease in volume of the egg, 

 increase of electrical conductivity, increased permeabil- 

 ity to certain intra-vitam stains, greater catalytic 

 power of fertilized eggs, increased permeability to alka- 

 lies, increase in rate of osmotic change with reference 

 to water. 



There can be no doubt that the permeability of the 

 egg increases at the time of fertilization in some cases 

 at least. On the other hand it is certain that this 

 change is less in some eggs than in others. No doubt 

 the great differences in vitality of unfertilized eggs of 

 different species are dependent, in part at least, on 

 such variations. Later on we shall discuss the role of 

 permeability changes in the complex of fertilization 

 processes. 



3. Changes in physical state. Many observers have 

 noted that changes in the physical state of the proto- 

 'plasm of the egg accompany fertilization. Thus the 

 eggs of Ascaris megalocephala, which have an irregular 

 outline prior to fertilization, become definitely spherical 

 soon after the entrance of the spermatozoon as the 

 fertilization membrane forms; on the other hand the 

 eggs of Nereis, which have a very regular contour before 

 fertilization, become decidedly irregular in outline fifteen 

 to twenty minutes after insemination, and gradually 

 resume the spherical state before the first polar body is 

 formed. A decided difference in the behavior of the 



