LM of a close up view of polarized pronuclei in a stage 1b embryo in vitro. The pronuclei have aligned perpendicular to the second polar body axis (double-headed arrow). This is the correct position for syngamy and the first cleavage.
From: Veeck and Zaninovic´, 2003. Reproduced with permission of the publisher, Taylor & Francis Group.
Source: The Virtual Human Embryo.