268 



GENERAL EMBRYOLOGY 



D 



FIG. 123. Changes in the structure of the egg of the Annulate, Choetopterus, 

 during and after fertilization. From Lillie. A. Axial section through fully 

 grown oocyte, still within ovarian epithelium. Ectoplasm in upper two-thirds of 

 egg only. B. Axial section through primary oocyte, ten minutes after extrusion, 

 three minutes after fertilization. Ectoplasm has already flowed to the vegetal 

 pole, leaving an exposed area of endoplasm at the animal pole. Part of the a 



