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1. The mid-intestine of Vanessa urticae has three separate categories of cells, interstitial cells, goblet cells, and ordinary columnal epithelial cells. 2. The interstitial cells renovate the epithelium by the addition of new cells at each larval ecdysis. 3. There is a period at the beginning of each instar during which cell differentiation occurs (from interstitial nests). This process soon ceases. Cell division by mitosis occurs amongst the interstitial cells throughout the instar. 4. No good evidence could be obtained that the goblet cells and columnar cells are homomorphous. The goblet cell cannot become a columnar cell because it undergoes a cycle of growth and differentiation which diverges increasingly from the columnar type. Similarly the goblet cells cannot be derived from senescent columnar cells because they are present at the time of hatching. Both are derived by independent modification of interstitial cells and are therefore dimorphous. 5. The goblet cells contain material which is optically indistinguishable from striated border. 6. It has been shown that in this animal the so-called merocrine method of secretion of the gut cells may not be a secretion process at all. The alternative view that the formation of ‘secretion’ vesicles is really a process of cell disintegration, due to wear and tear, or to the incidence of metamorphosis, is here favoured.

On the Development of the Mid-Gut in the Larval Stages of Vanessa urticae (Lepidoptera)