Aresearcher is looking through a microscope at a petri dish full of mouse embryos. these embryos appear as balls with no indentations along their surfaces. these embryos are most likely:

These embryos are most likely in the morula stage. The morula is an early stage in embryo development consisting of 16 cells in a ball shape. The marula resembles a mulberry, and is produced through a series  of cleavage divisions starting from the single-celled zygote. After this stage, the embryo will start showing more distinct features with the formation of desmosomes and gap junctions, and eventual formation of organs.