Re-examination on the evolution of embryonic membranes in the Atelocerata, with special reference to the functional specialization

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Phylogenies of the atelocerates and hexapods have been developed, based on their embryonic membranes. However, these phylogenies seem to have been misleadingly brought about from the insufficient or erroneous observational data, and I started to study- in detail the embryonic membranes of the animals on which careful investigations were needed but wanted, i. e., the Microcoryphia and Thysanura, so as to extend the comprehensive discussion on the evolution of atelocerate embryonic membranes.Achievements produced in this study are as. follows, and they are published into one review and four original papers.1. The embryonic membrane fold of microcoryphians is qualitatively to be serosal.2. The serosal fold in the Microcoryphia is to have been acquired in the evolution, as a sequel to the renounce of the ability for secreting the cuticular egg envelope by the embryonic area, which should have occurred in the course of ateloceratan evolution, The condition of embryonic membrane fold in the Microcoryphia may be read as the "preadaptation" to the amnioserosal fold shown in the Thysanura-Pterygota.3. There is no evidence that the yolk fold in the Microcoryphia is homologous to the amnioserosal fold in the Thysanura-Pterygota : these folds have been phylogenetically correlated with each other.4. The succession of functional specialization between the embryo and embryonic membranes through the atelocerate evolution can be recognized as : Myriapoda* Collembolans/Diplura*Microcoryphia*Thysanura-Pterygota.5. The amnioserosal fold in the Thysanura-Pterygota appears to have the functional role of secreting a serosal cuticle beneath the embryo as the principal one, as the embryonic membrane fold in the Microcoryphia.6. The condition of embryonic membranes of a thysanuran Thermohia domestica has been accepted to represent the ancestral, but it proved to be not ancestral but derived or autapomorphic.