Gut morphology of Mastotermes darwiniensis Froggatt (Isoptera : Mastotermitidae)

The digestive system of Mastotermes darwiniensis (Isoptera : Mastotermitidae) is similar to that of other lower termites. The cuticle in the proventriculus of the foregut is sculptured into 6 large dentate plates. Large setae are dispersed over the 1st and 2nd order folds and small setae are on the 3rd order folds. Epithelial cells in the foregut are of one type. The midgut cells are of one functional type, with 3 stages of the developmental cycle clearly distinguishable at any one time. There is no close association of mitochondria with the apical plasmalemma or microvilli. The epithelium rests on a basal lamina and has regularly distributed regenerative crypts. The midgut cells contain a large number of mitochondria close to the basal plasmalemma. Invaginations of the basal plasmalemma are very extensive and small tracheoles are plentiful close to the basal lamina. The presence of rough endoplasmic reticulum, most of which exists in the supranuclear cytoplasm, indicates that protein synthesis occurs in these cells. An abundance of basal plasmalemma invaginations is indicative of some fluid transport occurring across the membranes. The malpighian tubules have accumulations of mineral concretion forms as well as glycogen. Tracheoles are fairly abundant and distributed around the tubules. Epithelial cells in the region where the malpighian tubules join the midgut contain granules which are presumed to be secretory. Dentate plates around the anterior colon entrance are oriented so as not to hinder the flow of the lumen contents towards the posterior colon. Invaginations of the apical plasmalemma of the normal paunch epithelial cell suggest that they are involved in fluid or solute uptake from the lumen. The cuticle of the hindgut consists of areas with adhering bacteria and areas showing an even distribution of pores free of bacteria. The epithelial cells of the anterior colon resemble those in the paunch. The epithelial cells of the posterior colon show 3 variations: a squamous-cuboidal cell with unconstricted lumen; a cuboidal-columnar cell type found at the constriction site close to the rectum; a second squamous-cuboidal cell type constituting the junction of the colon and the rectum. This last cell type shows an abundance of cytoplasmic microtubules and a thick subcuticular zone.