148 PROBLEMS OF FERTILIZATION 



measured by Glaser (1914); individual eggs of Arbacia 

 were measured before and after fertilization, and in 

 nearly all cases a measurable decrease in diameter was 

 recorded, in some cases as much as 10 per cent. In 

 the starfish the decrease was found to be still greater. 

 The contrary results of McClendon (1910) on Arbacia 

 may be interpreted as due to the great indrv idual varia- 

 tions in size of the eggs, which were measured in a 

 statistical and not in an individual way. 



Loeb (1908) believes that to explain the tension of 

 the fertilization membrane (in Strongylocentrotus) it is 

 necessary to assume some slight loss of colloids from the 

 egg at fertilization, but he was unable to detect any 

 measurable difference in the diameter of fertilized and 

 unfertilized eggs. Okkelberg (1914) has determined by 

 careful measurements of individual eggs that fertiliza- 

 tion produces an average decrease of 13 .48 per cent in 

 the volume of the eggs of the brook lamprey. He 

 thinks that the substances lost include some colloid 

 material. 



The increase in permeability resulting from fertiliza- 

 tion has also been tested in other ways. McClendon 

 (1910) demonstrated an increase of electrical conductiv- 

 ity as a result of fertilization or action of partheno- 

 genetic agents in the egg of Toxopneustes; he determined 

 the resistance (reciprocal of conductivity) of unferti- 

 lized eggs to be 595 ohms and that of the same eggs 

 after fertilization to be 455 ohms; from this he argues 

 that the egg becomes more permeable to ions, on which 

 the conductivity depends, at the beginning of devel- 

 opment. Gray (1913) made similar determinations. 

 Lyon and Shackell (1910) have also shown that eggs 



