THE PERCEPTION OF FORM 



661 



environment which can only be explained by the possession of a 

 considerable degree of form vision and sufficient appreciation of the 

 meaning of objects to influence their ordinary activities. 



Some AMPHiBiAXS, such as the frog and toad, are essentially 

 visual animals ; they catch their insect food with great dexterity, a 

 feat demanding considerable visual acuity, and recognize their mate 

 by sight several inches away (Banta, 1914). Moreover, there is some 

 evidence from their homing ability and capacity to recognize their 

 LviTKor} .\:^t their behaviour is determined to some extent by 

 visual memory although other senses undoubtedly contribute, some- 

 times to a prejjonderant degree (Breder, 1925, in HyJa ; Czeloth, 1930, 

 in Triturus). The inertia and lack of intelligence of Amphibians, however, 

 make experimental exj^loration of their form-sense difficult. On the 

 whole it would appear to be defective : in this respect they are much 

 inferior to fishes. Thus frogs have been found to be unable to 

 distinguish between a lighted space and a white solid ; trained to the 

 former they would attempt to struggle into a solid white surface 

 (Dickerson. 1906) ; but Pache (1932) was able to train Hyla to 

 distinguish between a triangle and a circle. It would seem that 

 movement -sight plays a much greater part than form-sight in their 

 visual activity both in natural surroundings and experimental training. 



Among REPTILES a high acuity of vision is seen only among 

 lizards and to a less extent among turtles. We would expect the 

 excellent fovea of lizards to provide a correspondingly good visual 

 acuity, an expectation borne out by the accuracy of their fiy-catching : 

 the unerring aim of the long tongue of the chameleon is proverbial.^ 

 With their cone-rich retinae the same applies to Chelonians ; thus a 

 turtle will deftly catch an insect in flight and a domesticated specimen 

 is said to recognize the person who feeds it at a distance of 50 metres 

 while paying no attention to a stranger (Rollinat, 1936). Moreover, 

 in training experiments turtles have been found to be able to dis- 

 tinguish between such forms as horizontal and vertical lines, circles, 

 triangles and squares or other simple geometrical figures (Casteel, 

 1911 ; Parker, 1922 ; Kuroda, 1933 ; Wojtusiak, 1933 ; Myhiarski. 

 1951). It would thus seem that these animals have a relatively 

 high capacity for form vision. On the other hand, the comparatively 

 crude nocturnal retinte of the Crocodilians and oi Sphenodon necessitate 

 a low acuity. Among the Ophidians the tree-snakes and bird-snakes 

 provided with a fovea - and binocular vision ^ are the only species 

 which depend essentially on their eyes in striking their prey ; but 

 the visual acuity of snakes as a class is probably the lowest among all 

 diurnal Vertebrates, mucli more dependence being placed on other 

 senses such as smell and touch. ^ 



1 p. 695. - p. 388. 3 p_ 674, 4 p_ 599, 



Hyla 

 Triturus (male) 



Chameleon 



Turtle 



