SENSORY ORGANS AND RECEPTION 357 



to warming by inhibition of the rhythm of impulse-discharge (Figs. 8.33, 

 8.34). These thermal responses occur throughout the physiological tem- 

 perature range from 3-20°C; sensitivity appears to be greatest in the range 

 of 10-1 5 C C. Temperature differences as small as 0T-O2 c C are detected by 

 these organs. After a response to a thermal change adaptation occurs. 

 Thus the ampullae are not absolute meters and can register only tempera- 

 ture changes. Lorenzinian ampullae appear to be rare in teleosts. 



Earlier behavioural studies indicated that teleosts can discriminate 

 temperature differences of around OT-TC. Employing conditioned re- 

 flexes Bull (20) determined sensitivity to thermal changes in marine teleosts. 

 Many species were found to respond to temperature increases of 

 0-03-0T0°C in the surrounding water. Species responding to an increment 

 of 0-03°C, the smallest change investigated, were Gadus merlcmgus, 

 Onos muste/us, Zoarces viviparus and Liparis montagui. 



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