Abstract:
The structure and function of the Malpighian tubules of the larva of the New Zealand glow-worm Arachnocampa luminosa (Myceto-philidae) have been investigated by electron microscopy and physiological methods. Electron microscopy methods included thin sectioning, histo-chemistry, and an investigation of junctional complexes by freeze-fracturing, osmotic disruption and tracer techniques. Ionic and electrical measurements were made on whole tubules as well as isolated regions to provide extra information on possible functions. The Malpighian tubules can be divided into four distinct regions: a short proximal region; a second enlarged region; a slender region closely associated with the hind-gut and a terminal distal luminescent region. Each region is composed of a different cell type, the structure and function of which can be correlated with physiological measurements. The successive parts of the tubule are postulated to function as follows: the first in potassium reabsorption, the second in secretion of primary urine, the third in absorption of nutrients from the hind-gut, and the fourth in light production. The results obtained are discussed in terms of current theories of Malpighian tubule secretion in insects.
