4-D images of a developing sea urchin gastrula (with DIC adjusted to show birefringence of developing spicules). Every 60 seconds, through-focal optical sections were acquired in rapid sequence ( 5 sec/stack of 104 frames) using stepper-motor-driven focusing controls on Shinya Scope 6, controlled by a Universal Imaging MetaMorph program . Out of the whole sequence, which lasted without interruption for 5 hours 20 minutes, four pairs of through-focal sequences separated approximately an hour apart are displayed here. See Article 42 (S. Inoue and TD Inoue 1986. Ann NY Acad Sci 483:392-404) in Inoue S 2008 Collected Works of Shinya Inoue World Scientific Publishing Co. Ltd. Hackensack, NJ pp 392-404.