The Gut and its Annexes
The three parts of the alimentary tract of Drosophila, foregut, midgut and hindgut, differ in origin. Fore- and hindgut are derivatives of the ectoderm, and as such are lined with cuticle; the midgut derives chiefly from the endoderm, although parts of the anterior midgut are of ectodermal origin (Technau and Campos-Ortega 1985; Hartenstein et al. 1985). In the fully developed embryo, the foregut consists of atrium, pharynx, oesophagus and proventriculus, with the salivary glands ending in the floor of the atrium, at its border with the pharynx (Fig. 7.1). The proventriculus is a complex structure, comprising an inner epithelial layer which essentially represents a continuation of the oesophagus; a recurrent layer which is folded back over the inner layer; and an outer epithelial layer which is continuous with the midgut (Fig. 7.2). The midgut is a convoluted tube that still contains yolk granules at hatching (see Fig. 2.41), and several parts may be distinguished from both topological and morphological points of view (Bodenstein 195o; see Fig. 7.3); additionally, four blind tubules called gastric caeca project from the initial portion of the midgut, at the base of the proventriculus (Figs. 7.2, 7.3). The hindgut has a dorsally directed ascendant portion, from which the Malpighian tubules originate, and a corresponding descendant portion that ends in the anus (Figs. 7.3, 7.6). A thorough description of the anatomical organization of the Drosophila larval gut, in particular of the intricate foregut, can be found in Strasburger (1932).
KeywordsMigration Depression Luminal Convolution Stein
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