AMPHIBIANS 



339 



».* 



Fig. 402. — The Iris of the Frog, Ra.\a. 

 Sliowing a large superficial artery ( x 500) (Xorman Ashton). 



The pKpil is nsuall}- circular in dilatation but on contraction takes 

 on varied shapes, sometimes round {Pipa). usually horizontally oval 

 (Rana), occasionally forming a vertical lozenge-shaped slit (the spade- 

 foot toad. Scapliiopus. Plirynomeriis, Ah/fes. Hykt. etc.) (Boulenger, 

 1890 ; Johnson, 1927 ; Mann, 1931 ; and others) (Fig. 4U3). Otlier 

 irregular shapes occur, such as the lieart-shaped jDupi^l of the fire-bellied 

 toad, BoDibinatcr, the diamond-shaj^ed j^ujiil of the large -fingered frog, 

 Ra7ia halecina, the semicircular j^upil witli the flat side uppermost of 

 the bull-frog, B. caiesbiana . or the pear-shaped pupil of Pelobafes (Figs. 

 403 and 404). The jDupils retain some of the autonomous activity 

 characteristic of Fishes, contracting on the direct stimulation of light, 

 and for tliis purpose the sphincter is lieavily pigmented so that its 



Figs. 403 and 404. — Aniran Pupils. 



00 



♦)(?)(? 



Fig. 403. — The typical pupils of various Amphibians in the contracted state 

 (right eye) ; when dilated all are circular, (a) The Javanese flying frog, 

 Polypedates reinwardti ; (b) Trachycephalus ; (c) the obstetric frog, 

 Alytes obsfetncans ; (d) Hyla vasta ; (e) the fire-bellied toad, Bombinator ; 

 (f) Pelohntes fuf!cus. 



Bomhinator 



in warning 



attitude 



Fig. 404. 



-The dilated (a) and contracted (b) pupil of the green tree frog, 

 Hyla ccpndra. 



