Investigations on the midgut caeca of mosquito larvae-II. Functional aspects.

Fluorescent dyes were used to observe antiperistaltic movements of the midgut which cause an anteriorly directed flow which provides the caeca with midgut fluid. Aminopeptidases could be demonstrated histochemically in the cells and lumen of the caeca. This would suggest that the caeca of mosquito larvae take part in the final degradation, resorption and storage of nutrients. The caecal membrane acts as a permeability barrier. Particulate material and substances which cannot be degraded or resorbed accumulate in the caeca. Moreover, the caeca are involved in osmoregulation. Changes in the number of mitochondria present in the microvilli of ion transporting cells occur. The number of mitochondria in the microvilli depends on the salinity of the culture medium of these larvae.