21. A zygote initially develops into a hollow sphere, called a blastula , which undergoes rearrangement and differentiation. 22. Epiboly in zebrafish is the first coordinated cell movement, and begins once the embryo has completed the blastula stage. 23. It includes a blastula , gastrula and a four armed echinopluteus stage that forms an important part of the zooplankton. 24. The first three to four months are spent with the blastula in suspended development before it implants itself in the uterus. 25. In the mammalian blastocyst ( term for mammalian blastula ) there are three lineages that give rise to later tissue development. 26. One concern is that blastula creation in SCNT-based human stem cell research will lead to the reproductive cloning of humans. 27. These fossils show the cleavage stage, and the blastula , but the identity of the adult forms is not yet unknown. 28. From the stage of having 128 cells, the embryo develops a cavity, the blastocoele, and is called a blastula . 29. The blastocyst must not be confused with the blastula ; even though they are similar in structure, their cells have different fates. 30. The anterior / posterior axis lies along the animal / vegetal axis set up during nuclei at the vegetal pole of the blastula .
