As the zygote undergoes cleavage, the number of cells increases but the overall size of each cell gets smaller. By the time the zygote reaches the 16-cell stage, it is called a

Morula.

Explanation:

A zygote is the product resulting from fertilization. During the journey of the zygote through the fallopian tubes, until its implantation in the uterus, it divides many times, thus going through different phases. From the 16 cells it is called a morula, this stage represents the set of cells from the division of the fertilized ovum, in the first stages of embryonic development. It represents an intermediate phase between the zygote and the blastocyst. The morula stage is characterized by the fact that the replicating cells are all the same size, and there is no differentiation of organs.

that scientist would be robert hooke

nucleus

would be most reasonable answer tbh