Sentence:  One form of clonal reproduction begins when a fertilized egg divides a few times in the womb before initiating embryonic development. In humans, this can lead nine months later to the birth of identical (monozygotic) twins. This phenomenon, known as <WSD>polyembryony</WSD>, occurs sporadically in many mammal species. However, only in armadillos does <WSD>polyembryony</WSD> happen consistently, in each and every pregnancy. 
Meaning of the word marked with <WSD> tags:  The production of two or more embryos from a single fertilized egg.