FERTILIZATION, CORTEX, AND VOLUME. 275 



the other two. For this reason, then, it is worthwhile to re- 

 examine the question and to decide if possible whether the egg 

 increases in volume, decreases, or remains constant. 



II. 



The question, unfortunately, has entanglements. Histo- 

 rically, as well as through needless misunderstandings, it is bound 

 up with the problem of the fertilization membrane. This 

 structure, despite the very clever criticisms recently made by 

 Garrey ('iQ 1 ) can be demonstrated on the surface of the unferti- 

 lized egg. After fertilization, the membrane demonstrates 

 itself a change brought about by easy stages in certain eggs. 



In Asterias, for instance, the membrane, at ordinary tempera- 

 tures, becomes visible rather slowly. In optical section, the 

 perivitelline space is noticeable first as a small clear crescent at 

 one point on the surface of the egg. From this region of initial 

 visibility, the narrow area spreads in both directions until the 

 horns of the crescent have met and completed approximately a 

 circle. At this moment the egg is no longer in direct contact 

 with the membrane whose diameter is now patently greater than 

 before. 



All this was implicit in my earlier statement ('13) in which I 

 wrote: "the egg peels itself away from the inner surface of a 

 thin preexisting membrane. This peeling away seems to depend 

 not upon changes in the fertilization membrane but upon changes 

 in the surface film of the egg. When this is rendered more 

 permeable, material leaves the egg and the egg shrinks away 

 from its closely adherent covering which then becomes visible." 



I applied the same interpretation also to iheArbacia egg though 

 its perivitelline space is very much smaller. Quite recently the 

 process of peeling has been very clearly described in Echinarchnius 

 by Just ('iQ 2 ). Chambers ('21) on the contrary, seems to have 

 misunderstood my meaning. I did associate a shrinkage of the 

 egg with fertilization and the appearance of the membrane; 

 however I did not claim for either sea-urchin or starfish an 

 exclusive monopoly of shrinkage or that "the initial diameter of 

 the completed fertilization membrane is equal to that of the 

 unfertilized egg" (loc. cit., . . ., p. 332). Indeed, I can discover 

 no relation between this statement and the facts, or my descrip- 



