VOLUMETRIC CHANGES IN EGG OF BROOK LAMPREY. 93 



Membranbildung keine mit dieser Methode wahrnehmbare 

 Volumanderung erfahrt. Das beweist mit Sicherheit, dass der 

 Inhalt des Membranraums hauptsachlich Seewasser ist, das 

 vom aussen in demselben diffundiert." 



In some work that I have done 1 on the fertilization process in 

 the brook lamprey, Entosphenus wilderi (Gage), I have obtained 



FIG. i. Unfertilized eggs of Entosphenus wilderi. 



results which indicate that the eggs in this form decrease consider- 

 ably in size after fertilization. 



Herfort 11 has given a careful description of the egg of Petro- 

 myzon fluviatilis and I have verified most of his observations on 

 the egg of the American brook lamprey. Since there is no 

 essential difference between the eggs of the two species, only a 

 brief description is necessary here. Before fertilization the egg 

 approaches very closely to an ellipsoid of revolution in shape 

 although it is slightly more pointed at the animal pole (Fig. i). It 



1 Presented to the Michigan Academy of Science at its nineteenth annual meeting 

 in Ann Arbor, April 3, 1913. Fifteenth Report of the Michigan Academy of 

 Science. 



2 Herfort, Karl, Arch. /. mikr. Anat., Vol. 57, 1901. 



