Investigations on the midgut caeca of mosquito larvae-I. Fine structure.

Four types of cells can be distinguished in the epithelium of the caeca of three species of mosquito larvae. Specialized cells secreting a 160nm caecal membrane occur either near the opening of the caeca into the midgut (Aedes, Anopheles) or in the posterior half of the caeca (Culex). The presence of chitin could be demonstrated in this membrane with wheat germ agglutinin. In larvae of A. aegypti and C. pipiens the posterior part of the caeca is occupied by ion transporting cells. In larvae of A. stephensi these cells are interspersed among other cells, even in the anterior part of the caeca. The ion transporting cells resemble other insect cells involved in osmoregulation. Their microvillar membranes are studded with 14 nm portasomes and are closely associated with mitochondria. The main type of caecal cell seems to be responsible for resorption and storage of nutrients and for the secretion of enzymes. Small and undifferentiated cells were observed sporadically and seem to be imaginal cells.