FERTILIZATION AFTER INITIATION OF DEVELOPMENT. 28 1 



show more than one sperm nucleus and this has usually under- 

 gone the characteristic swelling and vacuolization changes of a 

 male pronucleus and is accompanied by an aster. After a 

 longer exposure to this concentration of hypertonic sea-water 

 the resemblance to sections of normal fertilization gradually 

 disappears and is superseded by a general condition of poly- 

 spermy and later by a non-reactive state of the egg substances, 



FIG. 3. X 3,000. Section of an egg exposed to the weaker hypertonic solution 

 for two hours and inseminated immediately on return to sea-water. Killed 20 

 minutes after insemination. All but one of the sperm heads are undergoing frag- 

 mentation. The egg nucleus does not appear in this section. 



with an abundance of spermatozoa, lying within the cytoplasm, 

 entirely unchanged. Of the eggs of AX 3 , probably the larger 

 percentage are polyspermic and show a reactive condition of 

 the sperm heads; they appear swollen and slightly vacuolated 

 and are usually accompanied by an aster more or less well formed. 

 Some sections of this lot still appear almost normal in their 



