128 INSECT PHYSIOLOGY 



logical theory, many of the activities of insects are described in terms 

 of inborn 'patterns of behaviour' which are called 'instincts'. 



Inborn patterns exist at all levels in the organism. The pattern of 

 growth is the outcome of the pattern of genes in the chromosomes. 

 The pattern of growth varies with time. The immediate cause of this 

 variation lies in the cycles of hormone secretion; and these cycles 

 may be correlated with changed patterns of behaviour. Other cyclical 

 changes, both in metabolism and in behaviour, are linked to the 

 twenty-four hour cycle of the terrestrial day. The twenty-four hour 

 (or approximately twenty-four hour) duration of these diurnal cycles 

 is inborn, and they will often continue for some days in completely 

 constant surroundings. But the initiation of a cycle is controlled by 

 cyclical changes in the environment, usually changes in illumination. 

 In the diurnal cycle of activity in Periplaneta, the immediate factor 

 which excites activity is a hormone circulating in the blood. This 

 hormone is the product of neurosecretory cells in the suboesophageal 

 ganglion; and the timing mechanism, or 'physiological clock', ap- 

 pears to reside in these cells. The nervous system, hormones, growth 

 and behaviour are thus closely interwoven. 



BIBLIOGRAPHY 



burkhardt, d. Adv. Ins. Physiol, 2, (1965), 131-173 (insect colour vision) 



DETHIER, v. g. The Physiology of Insect Senses, Methuen, London, 1963, 

 255 pp. 



goldsmith, t. h. Physiology oflnsecta I (Morris Rockstein, Ed.), Academic 

 Press, New York, 1964, 397-462 (insect vision: review) 



harker, j. e. The Physiology of Diurnal Rhythms, Cambridge University 

 Press, 1964, 114 pp. 



haskell, p. t. Insect Sounds, Witherby, London, 1961, 189 pp. 



huber, f. Physiology oflnsecta II (Morris Rockstein, Ed.), 1964, 333^406 

 (integration by the central nervous system in insects) 



LiNDAUER, m. Communication among Social Bees, Harvard University Press, 

 1961, 143 pp. 



ruck, p. Ann. Rev. Entom., 9, (1964), 83-1 02 (structure of insect retina: review) 



schwartzkopff, J. Physiology oflnsecta I (Morris Rockstein, Ed.), 1964, 

 509-561 (mechanical sense organs: review) 



slifer, e. h. Int. Rev. Cytol., 11, (1961), 125-159 (fine structure of insect 

 sense organs: review) 



thorpe, w. h. Learning and Instinct in Animals, Methuen, London, 1962 



wigglesworth, v. b. The Principles of Insect Physiology 6th Edn., Methuen 

 London, 1965, 156-186 (nervous system); 187-223 (vision); 224- 

 272 (mechanical and chemical sense organs); 273-316 (physiologi- 

 cal mechanisms of behaviour) 



