I'm in DC currently and trying to make regenerative mixture for the final fight, but I have never seen a "blastema" anywhere. I looked it up on the wiki and it says they are dropped by Deep Worms. I killed every single Deep Worm in the labyrinth and none of them dropped anything other than an acid gland, not one.
So maybe I have the worst luck in the world, but here's the thing: this is my second playthrough of Deep Caverns, and on my first one, I ALSO killed every single worm in the maze, and they ALSO never dropped a single blastema. My luck can't be THAT bad, can it?
So assuming the wiki is right (is it?) that this organ does indeed come from Deep Worms, the drop rate of the blastema needs to be adjusted, because right now it's possible to kill every worm and not get a single one.