92 ^SPECIAL CONVERGENCE 



nocturnal in their habits, the pupil of the eye 

 becomes contracted in a bright light to a narrow 

 aperture which may retain its normal and primitive 

 circular shape or may become a vertical ellipse 

 or a narrow vertical slit or a horizontal ellipse or 

 slit. The pupil of the cat's eye is round at night 

 time, vertically contracted during the day ; the 

 leopard's eye and the jaguar's, on the contrary, 

 like the lion and tiger, contract in bright sun- 

 light to a circular pinhole aperture. Mr Frank 

 Buckland has noted that the pupil of the fox's 

 eye behaves, not like the dog's, as one would 

 expect, but like the cat's, and this linear pupil is, 

 by some writers, 1 advanced as a generic character 

 of the genus Vulpes, as distinguished from Cants. 

 Amongst tailless Batrachia (frogs and toads) 

 the most extensive genera, Rana, Bufo, Rhaco- 

 phorus and Ixalus, have a horizontal pupil, a 

 vertical pupil being the exception in this division. 

 Geckoes (Geckonidae), the lizards of tropical and 

 subtropical countries which can run along upright 

 and over - hanging surfaces by virtue of the 

 adhesive pads on their digits, have the vertical 

 form of pupil ; when partially contracted the 

 margin of the iris in some species is crenulated ; 

 and when quite contracted so that the anterior 

 and posterior borders are in contact, leaving only 

 a vertical pupillary suture between them, the 



1 E.g., E. T. Seton, " Life-Histories of Northern Animals." New 

 York, 1909, 2 vols. 



