PUPIL OF THE EYE 93 



latter has a beaded appearance, the beading 

 corresponding with the previously noted crenula- 

 tions. Crocodiles also show the narrow vertical 

 pupil. 



Among snakes, round and vertical pupils occur 

 with nearly equal frequency, the former rather 

 more frequently than the latter ; but Dryophis, 

 called the whip-snake, has a very pronounced 

 horizontal pupil (Fig. 6). 



FIG. 6. 



Head of Dry aphis pulverulentus in side view. 



In the class Mammalia the round pupil pre- 

 vails, whereas the vertical pupil, as mentioned 

 above, characterises certain groups. The oblong 

 horizontal pupil of the horse, camel, ox, and sheep 

 was referred to by Owen in his " Anatomy of 

 Vertebrates" (1866); it is very sharply defined 

 in goats that have a gilt-edged iris. Owen also 

 stated that in a dead Agouti (Rodentia) the 

 pupil was a horizontal ellipse ; but he did not 

 allude to the horizontal pupil of the mungoose, 

 nor have I seen it mentioned in any other work 

 so far as I can remember. In the Civet family 

 (Viverridae), which is closely allied to the Felidae, 

 the vertical pupil appears to be the rule, but 



