Free-flowing cells and those that are stuck together?

[SheffJoe]

I've just been thinking about the development of an embryo from the zygote stage. How is it that when cytokinesis takes place, the cells all stick together in a little ball? But then, later in life, some are not bound to others (red blood cells, sperm cells, etc.). How is it that some cells are stuck together and some are separated? How does this develop?

[plasmodesmata11]

http://en.wikipedia.org/wiki/Extracellular_matrix
That link talks about the extracellular matrix... hopefully it will help you answer your questions!

[JorgeLobo]

In reference to embryo development - the dividing mass of cells is initially held within a membranous structure - zona pellucida - that is eventully breached shortly before implantation. It has more than a mechnical function as it's involved in sperm binding.