THE LIFE-HISTORY OF NUCULA DKLPHINODONTA. 317 



eggs tliafc have not been fertilised. Eggs were sometimes 



obtained tliat 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 



//« a 



fii 



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

 Nucula delphinodonta. 



its appearance on the side of the ^^^ 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 tlie first time. It is possible that some sperm were in tlie 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. 



