In Just 27 Hours, There Have Occurred Thousand of Cell Divisions, and Cells Are Organizing

In just 27 hours, there have occurred thousand of cell divisions, and cells are organizing in regions where they become specialized and begin forming specific parts and organs of the body. All of this is happening inside of the semi-permeable egg membrane, protected from the outside elements, bacteria, etc. It is a semi permeable membrane because water molecules can go in and out and oxygen can go in and CO2 can come out, etc.

At around 44 hours, there is a functioning heart and the beginning of a circulatory system, and who knows what other organs are already functioning. If you see a video I took at this stage (see below) you will see the pumping of its heart. If the heart is pumping, there must be blood and blood vessels. I think of the significance of a functioning heart at this point in the development of the fry.

At 48 hours the embryos have ruptured the egg membrane; the original cell membrane of the egg cell. This means that the embryo now has a skin layer enclosing it. Look at the black cells (that is what these are) in the back side of the egg yolk (abdomen) and tail. If you follow the tail forwards in this photo, you can clearly see the outline of the body of the developing fish all the way to what is becoming a mouth