Figure 6

Histological analysis of the ovary and carapace. (A,B) Ovarian eggs in a control individual. (C) The nuclear envelope was invisible in controls before moulting. (D , E) A meiotic apparatus found in ovarian and ovulated eggs of controls, respectively, and (F,G) ovarian eggs of a 20E-treated individual. (H) The nuclear envelope had not degenerated in the ovarian egg in the 20E-treated individual that neither moulted nor ovulated. (I) A division apparatus appeared and chromosomes aligned at the metaphase plate in the 20E-treated individual that moulted normally but did not ovulate. This meiotic apparatus at metaphase was also seen in the control eggs released into the brood pouch immediately after ovulation. However, in the 20E-treated individuals, meiosis stopped at metaphase and did not proceed. (J,K) Carapace formation in controls and (L,M) 20E-treated individuals. (J) A carapace layer with a newly formed carapace underneath the old one formed before moulting in the control. (K) A new carapace was observed immediately after moulting in the control. (L) A new carapace was also formed in the 20E-treated individual that neither moulted nor ovulated, and (M) the 20E-treated individual that moulted normally but did not ovulate. Yg: yolk granule, No: nucleolus, Od: oil droplet, Ne: nuclear envelope, Cp: carapace. Tissue sections of exogenous 20E-treated and the control adult female D. magna were stained with hematoxylin and eosin.