On the seventh day, C147 was chosen. Before this, she had just been another face in the rapidly growing crowd of cells in a featureless circular room, but on that day she realized she was different. She'd been helping the others push the room along - they'd been taking turns pressing their bodies against the curved jellylike wall on one side, causing the whole thing to roll forward like a gigantic beach ball with them trapped inside, walking on an endless treadmill to keep the floor underneath them. It wasn't pleasant, and C147 wondered whose idea the whole thing had been, or how they were even sure it was what they needed to do.

In the middle of one particularly hard push, C147 gasped and doubled over, pressing a hand to her chest. A strange feeling had suddenly come over her - a stab of something that was almost pain, but yet somehow more pleasant? It felt like potential, like a secret message about her future that only she could hear. She was meant for something great, she just knew it. As the warm feeling spread through her limbs, she stood up and gazed around with new purpose.

"What's the matter?' asked C32, one of the older cells who had been a direct precursor of hers a couple generations back. "Gene expression or you gonna divide already?"

"Uh… expression, I think."

"Well," shrugged the older cell. "You don't look any different. Get back to work."

It seemed a little unfair to C147 how C32 had just brushed her off, but she shrugged and continued pushing. She'd only existed for a day or two, but somehow she found herself bored already. Even if she looked the same, she felt different now, suited for more than a life of pushing the wall or sitting there dividing endlessly. Someday she'd show C32 and the others that there were more interesting things to do in the world. Not that she knew what she was supposed to do exactly, but she hoped she would find out soon.

On the tenth day, C147 stepped back and admired her handiwork. She and some other cells had just finished dividing their apartment into two separate rooms and reinforcing the outer walls, and just in time too. The thick wall she'd been pushing against for days had suddenly split open, and the cells had been left with just the hastily-constructed material they'd erected themselves to separate them from the outside world. It looked a little thin and patchy, but she trusted the TEs who'd taken charge of building it - if they said it would hold, it would.

According to C8, one of the real old-timers, the TEs had been just like them at one time, but somehow they had known it was time to change, to get all tall and skinny and specified. "How did you know?" C147 asked of TE59, who stood facing the wall, flexing his long fingers impatiently as if waiting for the next task to present itself. "How'd you know what to do?"

"Barely done anything yet," was TE59's cryptic reply. "But I just knew. It was actually my progenitor that got decided - he divided and I was born, and, well - here we are," he waved a hand to indicate the wall, his life's work thus far.

Just then, there was a sudden thud, a bump hard enough to make the room shake, and then a long drawn-out scraping sound against the same side of the wall TE59 had just pointed at. C147 jumped, wondering if the other cell had caused this somehow, but TE59 looked just as startled as she did. And then another TE - 68, maybe - slapped him on the shoulder and handed him a pickaxe.

C147 watched with eyes the size of saucers as the two trophoectoderm cells turned around and began happily demolishing the wall they had just built.

"What are you guys doing?" C147 yelled, and started to run toward them, when another cell suddenly grabbed her from behind.

It was PGC3, one of her own progeny, but the kid was so much more calm and composed than C147 right now that it almost made her seem older. "It's okay, chill. I'm sure they know what they're doing. Just like we do, right?" And with that the younger cell winked at her, smiling in a way that was almost smug. "Besides, some of the new peeps and I were talking. They said not to hang out with the TE's, because they're not real cells anymore. They're not gonna be special, like us PGCs. And I heard their jobs are just temporary, like they're gonna be out of work sooner or later."

"What are you talking about?" C147 asked her progeny, unable to tear her gaze away from the TEs' systematic destruction of the wall. The thin planks were beginning to separate, revealing another layer beyond them. What was it? Shortly after the original wall had broken down, their room had fallen off the road they'd been rolling along, and ever since then they had just been floating through space with nothing around them save what they themselves had built. But just now they'd bumped against something, yet another wall that was colored a bright vibrant red and seemed to be pulsating slightly...

"Who said the TEs were temporary?" C147 continued, forcing her attention back to PGC3. "And we don't even know what our own jobs are. Plus… what do you mean, 'us' PGC's? I thought there were only a few of you guys, but I'm not…"

PGC3 only smiled cryptically and handed her a small hand mirror. With a gasp, C147 saw that the white name tag stuck to the chest of her own uniform had… changed, somehow. She wasn't sure when it had happened - maybe during that weird surge of gene expression a few days ago, and C32 had either just not seen it or chosen not to comment? Or maybe it was when she divided, or…

PGC3 broke into a shallow curtsy, a gesture halfway between serious and sarcastic. "All hail to PGC1, the first of her name."

Note:

PGC = Primordial Germ Cell (what it does might be a spoiler, so look it up)

TE = trophoectoderm, which are the cells that will later make the placenta

What's happening here in biology terms, is the embryo got fertilized about a week ago, and now it's a blastocyst (hollow ball of cells) that is rolling along the fallopian tubes and then implanting into the uterus.

Hope you like it! :) Will try to continue as the inspiration strikes lol, was using this as an excuse to avoid *actually* studying early embryology.