FERTILIZATION, CORTEX, AND VOLUME. 277 



Under similar conditions the Asterias ovum changes markedly. 

 The freshly shed egg is often pear-shaped and frequently flat- 

 tened. It approaches the spheroid condition in the course of an 

 hour in sea-water and it is then possible to select eggs not dis- 

 tinguishable from spheres. It was with such that I worked; 

 they had established equilibrium and consequently were treated 

 exactly like those of Arbacia. But in order to be consistent, I 

 must assume that here again there was some flattening by weight 

 and so for both sorts of eggs the question to be answered is the 

 same: How much of the apparent decrease in diameter is the 

 result of a change in shape and how much is indicative of an 

 actual loss in volume? 



The magnitude of the loss w r hich I reported for Asterias is 

 much greater than that found in Arbacia. However, all except 

 tw T enty-five of my original measurements were based on the sea- 

 urchin egg. In my search for further evidence, I therefore 

 limited myself entirely to the second type. 



The methods employed differed somewhat from the technique 

 of Chambers. As before I limited myself to the period of actual 

 fertilization. In these newer measurements I again preferred the 

 stage micrometer to one of the ocular type. I also did not 

 pierce the chorion with a needle or roll my eggs on gelatin plates 

 in order to remove the jelly. In the absence of proof to the 

 contrary, these procedures cannot be considered innocuous on 

 account of the high salt content of the chorion ('22). In fact I 

 used the chorion in order to avoid all possibility of discoidal 

 distortion. This was accomplished by entangling the jelly on the 

 minute fibrils of a slightly roughened cotton thread. In this way 

 it is easily possible to prepare depression slides on which a 

 considerable number of eggs have been ensnared by several fibers 

 each one sticking to the jelly at a single point. This method 

 has several advantages; the eggs remain "afloat" and move in 

 the liquid whenever the fibrils bend; without being in contact 

 with a solid surface, every egg if desired can be identified by its 

 position along the thread; the attachment of the fibers at several 

 points in the chorion corrects any distortion that might result 

 from suspension at only one point. Furthermore the eggs in 

 these preparations can be made to yield accurate records of 

 volume and shape by projection in the form of silhouettes upon 



