Final answer:
During the first month of embryonic development, the heart beats and several organ systems begin to form. However, ossification does not occur during this time.
Step-by-step explanation:
The first month of embryonic development involves several major developments, including the formation of organs. However, one development that does not occur during this time is ossification, which is the process of bone formation. Ossification typically begins later in embryonic development or during the fetal stage.
During the first month of embryonic development, the heart begins to beat and pump blood, the eye pits and limb buds start to form, and the rudiments of the pulmonary system develop. These processes are critical for the establishment of the body's structures and systems.
In summary, the 1st month of embryonic development encompasses various important developments, but ossification does not occur during this time. Some key developments include the beating of the heart and the formation of the eye pits, limb buds, and pulmonary system.