How does biodiversity occur?

How does neurulation occur before gastrulation even complete?

• I understand that body folding can occur before the whole process of neurulation completes, but how does neurulation occur before even gastrulation completes its cycle? doesn't all the layers of ecto/meso/endo have to form first before the ectoderm starts the formation of the notochord which signals the neural tube to form? i have read in many sources that these two processes occur pretty much in a linked process, but I have trouble understanding. can neurulation occur within an embryo without having gastrulation complete around it?

• Answer:

  Best to ask this question in the Biology section..