Microaquaria for time-lapse cinematographic studies of morphogenesis in swimming larvae and observations on sea urchin gastrulation

A technique is described which permits a time-lapse cinematographic analysis of morphogenetic processes of sea urchin larvae and other marine larvae, the rapid swimming movements of which normally prohibit the use of time-lapse recording. The method has been applied to the gastrulation of the sea urchin Psammechinus miliaris in time-lapse experiments on single larvae for periods up to 12 hours with little disturbance of the normal development. A preliminary analysis of the film focuses attention on contractile pseudopodia as operative units in gastrulation. Such pseudopodia mediate the migration of the primary mesenchyme cells. Pseudopodia are also active in a second phase of invagination of the archenteron. During this phase, pseudopodia are formed by the cells in the tip of the archenteron rudiment. By the contraction of these pseudopodia, which attach themselves to the ectoderm, the archenteron tip is pulled in the animal direction.