Revised Procedure 1. Obtain adult sea urchins, species, Lytechinus variegates. 2. Harvest the gametes from these sea urchins using 0.5 M KCl injections (2mL.). Using a needle, piece the ventral side of the embryo, injecting small aliquots of KCl into each of the five symmetrical regions of the sea urchin. Gently agitate the sea urchin. 3. Observe the expulsion of the gametes to determine whether they are eggs or sperm. Collect eggs in a beaker filled with ASW and sperm in a dry petri dish. 4. Allow the sea urchin eggs to settle to the bottom of the beaker, remove the supernatant and wash the eggs with ASW containing PABA in order to prevent the hardening of the fertilization envelope. 5. Allow the sea urchin eggs to settle again, and repeat this washing process two more times. 6. Once the eggs have settled to the bottom of the beaker, pour off the PABA and replace with ASW. 7. Separate eggs into four samples of approximately similar size. Label the groups as follows: "control", "two-cell twinning", "four-cell twinning", and "eight-cell twinning". 8. In ASW, introduce the sperm to the eggs. 9. Observe the groups for cell divisions. 10. Once the "two-cell twinning" group has completed the first division, transfer the embryos to a hypertonic solution. Then pass the embryos through fine nylon mesh to separate blastomeres. 11. Return these embryos to ASW and allow them to develop. 12. Once the "four-cell twinning" group has completed the second division, transfer the embryos to a hypertonic solution. Then pass the embryos through fine nylon mesh to separate blastomeres. 13. Return these embryos to ASW and allow them to develop. 14. Once the "eight-cell twinning" group has completed the third division, transfer the embryos to a hypertonic solution. Then pass the embryos through fine nylon mesh to separate blastomeres. 15. Return these embryos to ASW and allow them to develop. 16. Observe and photograph all of the embryos at the "zero hour" after twinning. 17. Allow the embryos to develop for twenty four hours. Observe and photograph. 18. Note any developmental differences that may have resulted from the twinning process.