1. No evidence was found that the larval ileum of the corn boners, Diatraea grandiosella and Ostrinia nubilalis, secretes a developmental hormone, "proctodone." 2. An abdominal ligature which isolated the ileum of diapause larvae of both species caused high mortality but did not retard the pupation rate. 3. Extracts prepared from the ileal epithelium of mature nondiapause larvae of D. grandiosella were injected into diapause larvae and did not cause premature diapause termination. 4. Marked cytological changes occurred in the ileum at the onset of metamorphosis. At times the ileal epithelium of both species displayed auto and acridine orange-induced fluorescence, characteristic of lysosomes. 5. An electron microscopic examination of the autofluorescent ileal epithelium of D. grandiosella revealed organelles which had typical lysosomal features and stained positively for acid phosphatase activity. 6. The secretory activity of the ileum can be accounted for by lysosomal involvement in its metamorphic reorganization, and by its osmoregulatory functions.