The planktic foraminifer Hastigerina pelagica (d'Orbigny) offers a unique opportunity to study ultrastructural changes during gametogenesis because of its precise timing of gamete release. In early stages of gametogenesis, annulate lamellae are formed at Golgi complexes. Here, endoplasmic reticulum is transformed into flat vesicles that become piled up in successive layers to form annulate lamellae. After formation the annulate lamellae are separated from the Golgi complexes and are moved toward the still undivided nucleus. Annulate lamellae are aligned in parallel layers at the nuclear envelope. Subsequently the foraminiferal nucleus separates into the gamete nuclei. Simultaneously the annulate lamellae disappear from the cytoplasm, presumably used as nuclear envelopes for the gamete nuclei. Because nuclear division occurs within a very short period of time, the synthesis of nuclear envelope material could be a limiting factor. Production of this material well before nuclear division allows this process to occur within a short time.