After the four-cell stage, not all cells are "totipotent" anymore. Therefore, identical (monozygotic) octuplets will not occur. Divisions continue, there will be more and more cells. This stage is called the cleavage stage, because little growth takes place, only division (the embryo does not grow yet). Of course, the amount of nuclear material will increase, because every new cell has a nucleus. The lump of cells consisting of blastomeres is called a blastomerula. There are approximately 30 cells that form a sphere, four days after fertilisation. This is called the morula, "mulberry". The diameter is virtually the same as the diameter of the blastomerula.
After about six days, the so-called blastula develops by forming a cavity, surrounded by 60 to 80 cells, which are 0.6mm in diameter. This cavity is the beginning of what will later become the digestive tract. The outer cells of the blastula are called trophoblast; these cells are the beginning of the placenta. In humans, implantation of the embryo takes places in the uterine wall at the end of the first week. Whether this moment also applies to cat embryos, I do not know.