Early development of
D. cylindrus. Shown are one unfertilized egg and three developing embryos at the eight-cell stage. Fertilized zygotes underwent holoblastic, equal cleavage through the 16-cell stage. The mode of gastrulation was not observed. Early cell divisions occurred at approximately 40 minute intervals. Embryos developed into swimming larvae in less than 16 hours. Scale bar represents approximately 0.5 mm.