THE PHYSIOLOGY OF FERTILIZATION 147 



2. Changes in permeability. --The increase in oxygen 

 consumption of fertilized eggs of the sea urchin indi- 

 cates a readier access of oxygen to the material of the 

 egg, and not a change in the oxidizable character of the 

 material, because the comminuted material of the unferti- 

 lized egg also consumes more oxygen than the intact egg. 

 The egg membrane must therefore be more permeable to 

 oxygen after fertilization than before in those cases in 

 which increase of oxidation after fertilization occurs. 

 There are several other evidences of an increase in perme- 

 ability of the egg membrane as a result of fertilization. 



Among these is the escape of substances from the 

 egg which previously escaped more slowly or not at 

 all. Carbon dioxide is an example of the first kind; 

 there is a sudden increase of CO 2 production at the time 

 of fertilization in the sea urchin corresponding to in- 

 creased oxygen consumption (Lyon). As an example 

 of the second kind the escape of pigment from the eggs 

 of Arbacia at the time of fertilization may be noted; 

 Lyon and Shackell (1910) have described this phenome- 

 non, which has also been observed by other investi- 

 gators. The extrusion of jelly from the egg of Nereis 

 previously described (p. 53) is another striking instance; 

 the egg of Ascaris megalocephala similarly excretes a 

 considerable amount of material at fertilization which 

 forms the thick resistant egg membrane of this form. 

 According to Reighard (1893) the egg of the wall-eyed 

 pike similarly excretes a substance from its cortical 

 layer at the time of fertilization, and the same is prob- 

 ably true of teleosts in general. 



Diminution in the size of the egg following fertili- 

 zation due to loss of materials has also been carefully 



