Fig. 1. Stages of early embryogenesis of the spider, Achaearanea tepidariorum. Photographs of living embryos at different stages are presented. These embryos were viewed from different angles to show morphologies characteristic of the given stages. Each embryo is schematically illustrated in the lower row. Asterisks indicate the corresponding site of the different stage embryos. White areas in the illustrations indicate yolk. Developmental schedule (at 25°C) is as follows: stage 1, 0-10 hours after egg laying (AEL); stage 2, 10-15 hours AEL; stage 3, 15-25 hours AEL; stage 4, 25-30 hours AEL; stage 5, 30-40 hours AEL; stage 6, 40-45 hours AEL; stage 7, 45-55 hours AEL; stage 8, 55-65 hours AEL. (A) Stage 1 embryo (about 5 hours AEL). Nuclear divisions occur deep in the egg. (B) Early stage 2 embryo (about 11 hours AEL). (C) Late stage 2 embryo (about 15 hours AEL). The energids reach the periphery of the egg, and undergo synchronous cleavages. (D) Stage 3 embryo (about 20 hours AEL). The energids shift toward one pole of the egg along the surface. (E) Stage 4 embryo (about 26 hours AEL). The energids settle and form a germ disc (large shaded circle). The primary thickening (small dark circle) is seen at the center of the germ disc. (F) Early stage 5 embryo (about 32 hours AEL). (G) Late stage 5 embryo (about 36 hours AEL). The cumulus appears from the center of the germ disc and moves straight to the rim (arrow). (H) Stage 6 embryo (about 42 hours AEL). The cumulus disappears, and the germ disc cells are rearranged migrating circumferentially (arrows). (I) Stage 7 embryo (about 50 hours AEL). The previous central region of the germ disc develops into the caudal lobe. Segmentation begins. Metameric morphologies are recognizable. The shape of the embryo is fan-like. (J) Stage 8 embryo (about 60 hours AEL). The germ band is formed, which elongates along the AP axis producing additional segments from the caudal lobe. a, anterior; p, posterior. Scale bar: 200 µm.

Return to article