INTRODUCTIONCtenophores, or comb jellies, are a group of marine animals whose unique biological features and phylogenetic placement make them a key taxon for understanding animal evolution. Because of its large size, fecundity, abundance in coastal areas, and recent introduction to European waters, Mnemiopsis leidyi (commonly called “sea walnuts”) is the most highly studied ctenophore. Under optimal conditions, these self-fertile hermaphrodites are capable of reproduction at 2 wk of age and can release up to 10,000 eggs per day. Adults can be maintained in large aquaria with gentle aeration as long as they are well fed and can be spawned daily; multiple generations can be raised in the laboratory. This protocol describes how to collect embryos from M. leidyi. Under natural conditions, spawning normally occurs ~8 h after sunset, such that eggs are released under the cover of darkness. Because spawning is triggered by the onset of darkness, keeping animals under an artificial light regimen in the laboratory can alter the time of spawning. This protocol is designed to induce animal spawning at approximately 11:00 a.m.; however, it can be adjusted for other times. The duration from spawning to hatching of larvae is 18-24 h.