Every human body begin as a single nucleated cell. This cell, known as the ovum, divides or segments and gives rise to a mass consisting of a number of similar units known as the morula. At this stage there are no distinguishable tissues.
Martin, H. Newell & Martin, Ernest G. The Human Body: An Account of Its Structure and Activities and the Conditions of its Healthy Working (New York: Henry Holt and Company, 1917) 29
Courtesy the private collection of Roy Winkelman