52 INSECT PHYSIOLOGY 



foodstuffs ; but whether this is generally true is uncertain. We have 

 seen that the greater part of digestion in wood-eating termites and 

 Lamellicorns takes place in the hind-gut, to what extent the pro- 

 ducts are absorbed here, or returned to the mid-gut, is not known; 

 but the hind-gut of Lamellicorn larvae has special areas of cells 

 which are believed to be concerned with absorption. 



Water is certainly absorbed in the hind-gut and rectum of many 

 insects (p. 63) ; and the food residue, in contact with the rectal glands, 

 may be converted to a more or less dry faecal pellet. 



Besides water inorganic ions are actively absorbed by the rectum 

 and this function is important in the regulation of osmotic pressure 

 and ionic composition in the blood (p. 66). In addition, amino acids 

 can be absorbed in the rectum of the locust Schistocerca, but whether 

 other substances besides water and inorganic ions are absorbed in 

 the hind-gut of most insects is not known. 



The faeces 



The excrement of insects varies in character from dry pellets to a 

 copious clear liquid, according to the amount of fluid in the diet. In 

 plant-sucking Aphids and Coccids it contains much unabsorbed 

 organic matter, particularly carbohydrates and amino acids; the 

 dried residue collects on the surface of plants to form 'honey-dew', 

 manna and such-like products. These insects take in phloem juice 

 which is under pressure in the plant, absorb perhaps no more than 

 half the amino acids and amides in the sap and even less of the sugar, 

 and excrete the residue containing a wide range of carbohydrates 

 that have been synthesized in the gut by the 'transglucosidase' ac- 

 tivity of invertase acting on the sucrose of the plant sap. 



BIBLIOGRAPHY 



house, h. l. Physiology of Insecta, II (Morris Rockstein, Ed.), Academic 

 Press, New York, 1964, 815-858 (insect digestion) 



lipke, h. and fraenkel, g. Ann. Rev. Entom., 1, (1956), 17-44 (insect 

 nutrition: review) 



treherne, j. e. Viewpoints in Biology (J. D. Carthy and C. L. Duddington, 

 Ed.), 1, (1962), 201-241 (absorption from the gut of insects: re- 

 view) 



