The mechanism of twins formation

   What events in pregnant woman underlie twins formation? What do zygosity, chorionicity and amnionicity depend on? It seems that the answer is very clear. As early as in 1955, the works by G.W. Corner were published, which served as the basis for proposing the traditional model of twins formation, still remains widely acknowledged. But whether is everything so obvious? In order to answer this question, it is necessary to go back to the roots and understand of how the overall idea about fertilization and formation of multiple pregnancies has evolved since the XVII century till the present time.