VOLUMETRIC CHANGES IN EGG OF BROOK LAMPREY. 



95 



circular perivitelline space is formed which extends around the 

 pole in the form of a groove. This groove widens rapidly towards 

 the animal pole until it forms a large space separating the egg 

 at this pole from the vitelline membrane. At the same time a 

 wave of contraction passes over the egg towards the vegetative 

 pole and within a few minutes the whole egg is separated from 

 the membrane. During the contractions of the egg, the long 

 and short diameters vary considerably from time to time. I have 



FIG. 2. Fertilized eggs of Entosphenus ivilderi. X6. 



made accurate measurements at short intervals which show that 

 the contractions are real and not merely apparent. They are 

 very striking and remind one of peristaltic waves or ameboid 

 movements. 



The whole process during which the membrane separates from 

 the egg lasts about five minutes and when the egg comes to rest 

 again it has assumed a spherical shape instead of the previous 

 ellipsoidal or ovoidal shape. During the process the vitelline 

 membrane becomes greatly distended. When the membrane 



