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Summary
A timetable of the embryonic development of Manduca sexta has been compiled to serve as a basis for physiological studies. Embryogenesis is complete within 117 hr at 24° C and was analyzed by examining specimens representing 20 stages, i.e. intervals of 5% of the total developmental time. Stage 0 denotes the newly deposited egg. Germ band formation, gastrulation, differentiation of tissues and organs, and blastokinesis are described in detail.
By stage 1 (6 hr post-oviposition) the cellular blastoderm is evident and the presumptive serosal and embryonic cells are distinguishable. At stage 2 the germ band has separated from the blastoderm, and by stage 3 it has elongated enormously, segregated the inner layer and is completely segmented. Subsequently, the segmental appendages differentiate: at first in the head, then in the thorax, and finally in the abdomen (prolegs). Stage 5 marks the onset of organogenesis while blastokinesis takes place at stage 8. A provisional but incomplete dorsal closure occurs as a result of amnion duplication. The embryonic membranes persist far beyond blastokinesis: the amnion until stage 17, the serosa until stage 19.
The serosa secretes two cuticles: the first serosal cuticle at stage 3 and the second serosal cuticle at stage 4. The embryo also deposits two cuticles: the first embryonic cuticle at stage 9 and the second embryonic cuticle (i.e. larval cuticle) at stage 12. The endocrine glands (prothoracic glands and corpora allata) differentiate at stage 7. The relationship between endocrine gland development, ecdysteroid titer and cuticle deposition is discussed.
