If the gut of Octopus vulgaris is ligated at both ends, the animal loses weight at about 10% per day at 21°C, dying after about 48 h. Ligation of the ducts to the midgut gland has the same effect. If one or both ducts are cannulated and led to the exterior with a sufficient length of duct remaining, sea water is taken up by peristalsis and there is little or no weight loss. As body weight falls, blood and urine osmolality remain unchanged, but blood conductivity falls and blood copper concentration rises, indicating a loss of salts as well as water. Muscle dry weight, as a percentage of muscle wet weight, increases as body weight falls. Octopus is hyperosmotic compared with sea water and the rate of ultrafiltration through the branchial heart appendages into the kidney sacs is estimated to be sufficient to account for the observed body weight losses.

Each side of the midgut gland, connected to the gut by a digestive duct, includes two distinct structures. One, the digestive gland, produces enzymes and is also concerned with absorption of the fluid and paniculate products of digestion. The other, the digestive gland appendage (the so-called ‘pancreas'), is composed of cells with characteristics that strongly indicate bulk fluid transport; it seems likely that this is the principal site of the fluid uptake. This evidently includes salts as well as water, since sea water taken into the gut (notably by rectal pumping) is not concentrated as fluid is withdrawn.

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