THE LIFE-HISTORY OF NUOULA DKLPHINODONTA. 317 



eggs that have not been fertilised. Eggs were sometimes 

 obtained that formed polar bodies and developed no further.^ 

 Just before each polar body is formed, a more or less 

 distinct, and frequently a very pronounced swelling, makes 



Text-figs. A, B, C, and D, — Early stages in the development of 

 Nucula delphinodonta. 



its appearance on the side of the egg opposite the point 



^ Most of the eggs of an isolated specimen of Nucula proxima, a form 

 that throws its eggs free into the water, formed the polar bodies, and a few 

 eggs cleft the first time. It is possible that some sperm were in the water, 

 but the water had not been changed for nearly twenty-four hours before the 

 eggs were laid, and sperm of this species do not seem to retain their vitality 

 for nearly so long a time. 



