EGG-VOLUME AND FERTILIZATION MEMBRANE. 59 



as has been pointed out by others, the eggs at one time may be 

 disks flattened vertically (Reighard, Chambers 8 ) and at another 

 time ellipsoids, or pear-shaped objects, suspended at one end of 

 their long axes, and yet at another time perfect spheres, then 

 there is an unrelated error among the observations that renders 

 them worthless. 



In the cases here studied there exists only the possibility of the 

 eggs being flattened vertically during the period before fertili- 

 zation and then changing into spheres after the fertilization 

 membranes are raised from the egg-cortex. This, however, 

 affects only the reduction observed in the inseminated Asterina 

 eggs. 



No one will doubt that the observed reduction in size of the 

 sand-dollar eggs during the bath in hypertonic salt represents a 

 real reduction in volume. If the effect of the osmosis is a gelation 

 there may have been a hardening of the egg-cytoplasm, but this 

 hardening of itself could not change the egg-mass from a spheroid 

 to a sphere. If the effect of the osmosis is an increase in surface 

 tension then such a change in form may well take place. 



The reduction in diameter of the inseminated Asterina eggs 

 during the first stage of cleavage is of the same order of magnitude 

 as was observed in the sand-dollar eggs in their hypertonic bath. 

 While some of this reduction may have been due to reshaping, 

 there also can be no doubt that some of it was due to loss of 

 material on the part of the egg-cytoplasm. This material, as 

 others have maintained, may be colloidal in part, but this obser- 

 vation supports the view that considerable water is given off from 

 the egg together with the colloid. 



It is remarkable that the percentage of swelling of the egg 

 treated to the hypertonic salt bath, after return to normal sea- 

 water, and the percentage swelling of the fertilization membrane 

 of the inseminated egg should both be of the same order of 

 magnitude. This swelling in neither case can be due to any 

 considerable extent to a reshaping of egg-substance. However 

 evident it is that the egg-cytoplasm of this parthenogenetic egg 

 has undergone a change in permeability different from the egg- 

 cytoplasm of the normally inseminated egg, it nevertheless 

 appears that the limit to extension in the one case is the same as 



