During development, the maturing ova are arrested during meiosis I (frequently at diplotene of prophase). Upon contacting sea water, the primary oocytes resume meiosis, the nucleus (germinal vesicle) is degraded, and the first and second polar bodies are formed by 1.5 and 2 hours, respectively. Fertilization can occur anytime during this time period.
- Plasma Membrane
- Nuclear Membrane