Histology of the Corpora Allata of Melanoplus differentialis (Orthoptera: Saltatoria)

1. The corpora allata of the grasshopper Melanoplus differentialis were studied histologically to determine whether these glands show changes related to their functions in the control of nymphal development and the production of ripe eggs and oviducal secretion. 2. Four classes of cells were recognized in the corpora allata of this insect: a, connective tissue and tracheal cells; b, undifferentiated cells; c, normal secretory cells; and d, giant secretory or polyploid cells. 3. The undifferentiated cells are small cells which divide mitotically and do not contain secretory granules or vacuoles. They show the greatest mitotic activity at the beginning of each developmental stage but occasionally divide at other times. 4. The glandular cells, both normal and polyploid, show characteristic changes related to secretory activity and inactivity which are fundamentally the same in nymphs and adults and in both sexes. During inactive phases they are reduced in size and resemble undifferentiated cells. During active phases they increase in cytoplasmic and nuclear volume, the cytoplasm becomes filled with strongly acidophil granules, then intracellular and finally intercellular vacuoles appear. At the height of secretory activity the appearance of the gland suggests that materials are flowing from central regions of the gland to the periphery. 5. In the fifth nymphal stage, at the end of which nymphal characters are produced, secretory material is elaborated throughout the intermolt period; active release of secretion occurs during the latter half of the stage. In the sixth stage, which terminates with the production of adult characters and metamorphosis, the glands show histological evidence of activity only during a brief period which begins on the second or third day after molting and ends around the middle of the stage. 5. The corpora allata are inactive on the day the grasshopper enters the adult stage, but the histological changes which lead to the production and release of secretory material begin immediately thereafter. Full secretory activity is achieved in the corpora allata of adult females shortly before the onset of the production of oviducal secretion and yolk. It is reached at an equivalent time in adult males.