From the Imaginal Cells series. http://jessedraxler.com/imaginal-cells
“After a caterpillar buries itself inside its cocoon, it waits to morph into a butterfly. The caterpillar does not simply shrink a bit and sprout wings. Instead, it sort of disintegrates into a puddle of ooze within the cocoon. If we were to open the cocoon halfway through the process, we would not find a half-caterpillar half-butterfly type creature, but a blob of goop. The goop is made up of a bunch of individual cells that are all basically the same type of oozy cells. For whatever reason, after the caterpillar has turned into ooze, a new type of cells start appearing. The original ooze cells are NOT changing into these new cells, but rather the new cells seem to come out of nowhere. They just appear out of thin air so to speak.
These new cells are called imaginal cells and they are so completely different from the original ooze cells that they are thought to be a virus or some other form of enemy so the ooze cells begin attacking the imaginal cells. However, even though the imaginal cells are being killed off for not fitting in, they still keep showing up, more and more of them. Eventually, the imaginal cells begin to find each other and cluster together. Like attracts like, and the clusters begin to join up with other clusters. The original ooze cells still keep attacking them but the imaginal cells continue to multiply and cluster together.
Eventually, they become a large community and they switch gears from simply being a group of like-minded cells into the programming cells of the butterfly. Some imaginal cells start changing into wing cells, some start changing into antenna cells, some start changing into digestive tract cells, and so on. They are no longer imaginal cells but become butterfly anatomy cells. As we all know, if left alone to do its thing, the butterfly eventually emerges as a completely new entity from the original caterpillar.”