Metamorphic changes in the hindgut of Sarcophaga ruficornis with special reference to the development of rectal pads

In Sarcophaga ruficornis, during normal metamorphosis the larval hindgut epithelium degenerates and the imaginal hindgut epithelium is formed from the proliferation and differentiation of the cells of the posterior imaginal ring. The newly formed hindgut becomes slightly dilated posteriorly to form the rectal pouch. At four places in this pouch, the epithelium becomes thick and forms the primordia of the rectal pads. The cells in the primordia begin to divide and project into the lumen of the pouch and later form the cortex cells of the rectal pads. The cavity of the primordia becomes filled with blood cells and fibrous material, which give rise to the medulla of the rectal pads.