The process of development is very complex with lots of possibilities for things to go wrong. What would happen if:

1. the sperm could not get into the egg?
2. the male and female pronuclei did not fuse?
3. DNA synthesis did not occur?
4. the centrosome did not align the chromosomes properly at metaphase?
5. the actual division was not competed or happened at the wrong location?
6. one cell was removed or damaged at the 2 cell, 4 cell, 8 cell stage?
7. at the two cell stage the two cells were separated and allowed to develop on their own? at the 4 cell stage?
8. hatching did not occur?
9. gastrulation went out instead of in?
10. skeleton failed to form in the pluteus?

Further questions for thought:

1. Why do cells with multiple chromosomes need the complex steps of mitosis to divide in comparison to the steps of binary fission in bacteria?
2. What are the adaptive advantages of external fertilization? What are the adaptive advantages of internal fertilization?
3. What are the adaptive advantages of external development? What are the adaptive advantages of internal development?