Dahlia Wartlet (sea-anemone) , 

 128; reaction to stimuli, 129 



Death's Head Moth, 71 



Deer : acuity of senses, 66 ; acuity 

 of hearing, 75, 85 ; excretion of 

 scent from glands, 107 



Diablotin, its use of sonar, 192-3 



Dogfish, 191 



Dogs: homing ability, 15, 226; 

 eyesight, 28 ; acuity of hearing, 

 84 ; location of sounds, 85 ; 

 scenting powers of sporting 

 dogs, 104-6; sense of taste, iii 



Dolphins, 210; use of sonar, 183, 

 187-8; reaction to Asdic, 187, 

 188; docility and playfulness, 

 188; sense of sinell, 198 



Doppler effect, 186 



Dormouse, experiment of scenting 

 power of, 107 



Dragonflies: visual acuity, 16, 34, 

 164; number of lenses in their 

 eyes, 23; observations on sight 



o^, 33-4 

 Ducks: scenting power, 19, 92; 



sense of touch, 1 14 

 Dugong, its sense of smell, 198 



Eagles, 148 



Ear(s) : mechanism and structure 

 in mammals, 169-73; of fishes, 

 1 74 ; of birds, 1 74-6 ; of reptiles, 

 amphibians, fishes, 177-8; com- 

 parison of vertebrates and in- 

 vertebrates, 1 78-9 ; of insects, 

 179-80; of whales, 190-1 ; pro- 

 prioceptive sense served by inner 

 ear, 219-23 



Ear-flaps. See External ears 



Earthworms : negative reaction to 

 light, 21, 22, 137; method of 

 catching, 32-3 ; as food for 

 newts, 44; responsive to touch, 

 119; their receptors for smell, 

 201 



Echo-location (sonar) : the prin- 

 ciple of, 1 82-3 ; animals that use 

 it, 183; its essence, 183-4; high 

 frequency of sound waves used, 

 184; by bats, 184-7; the Dop- 

 pler effect used by certain bats, 

 186; by whales and dolphins, 

 187-91; by the Ostariophysi, 



INDEX 233 



191 ; by birds, 192-3; use of an 

 electric field to probe surround- 

 ings, 193-4 



Echo-sounder, 182 



Edible Frog : observations on sight 

 of, 39-40; territorial defence 

 behaviour, 77 



Electric currents, reaction of fishes 

 to, 216-17 



Electric eel, 193, 194 



Electric organs, of fishes, 193 



Elephant : hearing of, 74, 84 ; 

 touch, 1 2 1-2; smell, 196 



Elephant Hawk Moths, observa- 

 tions and experiments on, 97 



Elliptical pupil, and nocturnal 

 vision, 28 



Eltringham, Professor, 167 



Emperor Moth : visual acuity, 1 6- 

 1 7 ; scenting power, 98 



External ears or "ear-flaps" 

 (pinnae) : possessed only by 

 mammals, 83, 170; of elephants, 

 84; of bush-babies, 86 



Eyed Lizards, 49 



Eye(s) : number of, in spiders, 23, 

 161 ; simple eyes (ocelli) and 

 compound eyes, 23, 160-7; 

 unique structure of chameleon's, 

 49-50; structure of, in higher 

 animals, 138; optical system of, 

 140-5; internal structure of a 

 bird's eye, 148; of molluscs, 

 157-60 



Feeding behaviour. See Movement 

 of prey 



Fer de lance, 215 



Fishes : sight : good sight of most 

 fishes, 18, 25-6; optical mech- 

 anism, 147, 152-3; in deep and 

 shallow waters, 15 1-2; colour 

 vision, 154; hearing: sensitivity 

 to vibrations, 73 ; possess only 

 an inner ear, 174; structure of 

 the ear, 177-8; use of sonar, 

 1 9 1-2; use of an electric field to 

 probe surroundings, 1 93-4 ; 

 smell: scenting power, 91-2, 

 99-100, 200; barely distinct 

 from taste, 205-6 ; taste : part 

 played by smell in, 1 10 ; touch : 

 response to vibrations, and the 



