FERTILIZATION, CORTEX, AND VOLUME. 28 1 



V. 



In accordance with these results then, the Arbacia egg by its 

 own weight, is capable of flattening in sea-water. This vindicates 

 the point made by Chambers. However, the extent of this 

 flattening is negligible for the issues here at stake. This is 

 shown by the measurements made under circumstances that 

 leave no room for discoidal deformation. On the other hand, 

 cylindroid distortion, when possible, may completely mask any 

 losses in spherical volume. 



We must now ask whether the loss here postulated anew for the 

 Arbacia egg, is unique and whether it articulates well with the 

 other facts of fertilization. 



I did not repeat the work on the starfish because the difference 

 there between the unfertilized and fertilized egg is even greater 

 than in Arbacia. For Nereis too, special measurements, merely 

 for the purpose of demonstrating a decrease in volume seem 

 superfluous because the elimination of a voluminous mass of 

 visible jelly is sufficient evidence. Again, according to Okkelberg 

 ('i4 2 ) the egg of the brook lamprey is subject to a similar loss on 

 fertilization. 



These cases, of course, do not imply that losses everywhere 

 must remain uncompensated long enough for us to measure them. 

 In certain instances, alterations in shape may offset actual de- 

 creases in diameter; in others there may be compensatory swelling 

 due to osmotic changes. Indeed, ultimately and no matter what 

 may be true at the moment of fertilization, the egg increases in 

 volume. The measurements which Chambers made 10, 20, and 

 even 70, minutes after impregnation have no bearing on the 

 immediate reorganizations of fertilization, however pertinent they 

 may be in a study on grow r th. 



But how do these losses in volume fit in with other facts 

 falling within the fertilization period? In an earlier paper on 

 egg-secretions ('i4 3 ) I compared the rates at which unfertilized 

 Arbacia eggs and eggs in process of fertilization discolor the sea- 

 water. The rates I found to be related as 2:3. During the 

 summer of 1922 I repeated these observations in another way. 

 On each of two small identical filters, I placed I cc. of a certain 

 preparation of dry shed eggs. To the one filter was added a drop 



of sea-water; to the other a drop of dry sperm. The contents of 

 19 



