pronucleus

In Asterias glacialis the most favourable period for fecundation is about an hour after the formation of the female pronucleus.

In Echinus, on the other hand, where the polar bodies are formed in the ovary, the male pronucleus is always small.

When it finally unites with the female pronucleus it is equal in size to the latter.

The tail in the meantime vanishes, while the neck swells up and forms the male pronucleus.

Selenka, who has investigated the formation of the male pronucleus in Toxopneustes variegatus, differs in certain points from Fol.