Ultrastructural changes of corpus allatum in the imaginal stages in the silkworm, Bombyx mori

Ultrastractural changes of the corpus allata during the imaginal stages were observed light and electron microscopically. Several characteristic changes of the corpus allata were found with the progress of time after the emergence. However, the ultrastructural differences of corpus allata between male and female moths were not markedly detected. The results obtained were as follows: 1) From just after the emergence, a large number of small vacuole are detected in the cytoplasm. After the emergence these vacuoles gradually increased in both number and size, occupying a great part of their cytoplasm. 2) The neurosecretory axons containing electron dense glanules are observed in both conective tissue envelope and cytoplasmic area. These granules increased from the 24th to 72nd hrs after the emergence, while the vacuoles increased in these axons. 3) Large numbers of mitochondria distribute in the cytoplasm, and their criste are clearly detected just after the emergence. These structures are however, disappeared gradually. 4) The nucleus contains many chromatin masses and nucleoli without any sign of synthetic activity. 5) The lysosome increases in the cytoplasm, and the basemembrane disorganized. These results indicate that the corpus allatum is clearly in the process of the histolysis during the imaginal stage.