Final answer:
A cell with a developing cleavage furrow is in the stage of cytokinesis, and it is likely an animal cell, as this process is part of the animal cell division where the cell splits into two.
Step-by-step explanation:
Observing a cleavage furrow through a microscope indicates that the cell is in the process of cytokinesis, which is the final stage of cell division. This event typically occurs in animal cells because they lack cell walls and utilize actin microfilaments to contract and divide the cell into two. A cleavage furrow is not seen in plant cells; instead, they form a cell plate during cytokinesis. One of the two new cells acts as a stem cell, entering its own cycle for future division, while the other becomes a functional cell, replacing an old cell in the tissue.