The alimentary canal of a representative species of soil-feeding termite was examined for associations with bacteria. Enumerations made in the principal regions of the intestine by direct observation and expressed for comparative purposes as total microbial standing crop showed a net three- to fourfold increase between the foregut (crop) and rectum. Filamentous organisms, putatively actinomycetes, contributed significantly to the flora in most regions of the gut and were more abundant, relative to non-filamentous forms, than in freshly ingested soil. Transmission and scanning electron microscopy of the gut wall showed that the actinomycetes formed novel associations with the host in the mesenteron, mixed segment and colon. Non-filamentous organisms, chiefly rods, colonized the walls of the first proctodaeal segment and the colon, in addition to filaments, and were present in large numbers in the contents of the third proctodaeal segment.

With 8 plates and 6 figures in the text)The morphology, histology and ultrastructure of the mesenteric and proctodaeal components of the mixed segment are described in detail, together with the disposition of the associated gut musculature, the patterns of peristalsis and the streaming movements of soil particles in the gut lumen. The mesenteric epithelium is characterized by very extensive basal infoldings which are associated with a large population of mitochondria, but evidence of significant protein synthesis and secretion is lacking. It is proposed that this tissue is a transporting epithelium whose major function is the secretion of a copious, K+ -rich fluid into the intestinal lumen to inigate the hindgut (proctodaeum) and that alkaline hydrolysis of humic fractions by this fluid is an essential component of digestion.Malpighian tubules are present, but do not participate in fluid excretion. Since the hindguts of soil-feeding termites are exceptionally voluminous and elongated and the major symbiotic micro-organisms occupy fixed positions by virtue of their attachment to the lining cuticle, it is argued that flushing is necessary to sustain microbial activity and for the recovery of end-products by the host. A survey of the protodaeal epithelium suggests that the anterior colon (P4a) is the most likely site of fluid reabsorption and that the wall ofthe hindgut anterior to this site is impermeable. The greater degree of ultrastructural differentiation of the mixed segment of Cubitermes severus and its more complete morphological separation from the midgut suggests that this species is a more advanced soil-feeder than Procubitermes aburiensis.

Electron microscopy of the hindgut showed that actinomycete-like bacteria were the principal microbial associates of two African species of soil-feeding termites. Elongated cuticular spines provided attachment.

No abstract

Mature columnar cells of the midgut of Cubitermes contain a prominent secretion product observed at light- and electron-microscopic levels. At the ultrastructural level the product is resolved as an electron dense material contained in vesicles up to 1 micron diameter that accumulate in the apical cytoplasm. The vesicles are composite, apparently formed by coalescence of at least two types of precursor vesicle both of which originate from the Golgi apparatus. Discharge of the product takes place by exocytosis into intercellular space at or in the vicinity of the apical septate junction complex. Augmentation of apical surface area by microvilli is less prominent in Cubitermes than in other termites for which data are available. This and other evidence suggests that absorptive functions are reduced in the midgut of this insect.