§ 5.321 



WATER BALANCE 



223 



Malpighian tubules (Fig. 5-18, upper specimen, and Fig. 5-19a, 

 dotted curve). If either the neck is Hgatured or the head is cut off, 

 preventing any flow of hormone to the body, or if the source of 

 hormone is removed by ablating the upper part of the brain, the 

 operated specimen swells steadily by retention of water (Fig. 



Fig. 5-18. Water uptake in larvae of the beetle, Anisotarsus cupri- 

 pennis. a. Normal larva, and h. operated larva to show the swelling 

 due to water uptake after removal of the upper part of the brain, 

 including the cerebral neurosecretory cells, and the corpora 

 cardiaca (from Nuiiez, 1956). 



5-18, lower specimen, and Fig. 5-19a, full curve). Injection of 

 brain extract restores the water balance, presumably by increasing 

 excretion (Fig. 5-19^, full curve); but extracts of suboesophageal 

 ganglion have no such diuretic effect (Fig. 5-196, dotted curve). 



The seat of action of this diuretic hormone does not seem to 

 have been established, but it acts on excretion rather than on water 

 uptake. Probably it inhibits the reabsorption of water as it passes 

 from the Malpighian tubules through the intestine. If so, a 

 decrease in cell permeability in the intestine could be responsible, 

 and w^ould be comparable with that occurring in the skin of 

 Carcinus, or in the distal kidney tubules of vertebrates, during 

 diuresis. 



One curious feature is that the secretion of this metabolic 



