THE CATS. 15 



younger the Cats the rarer the cases in which the pupil is 

 round ; and, conversely, the older the Cats the greater the 

 prevalence of round pupils. This, I think, may be due to a 

 decrease of the elasticity and consequent contractility of the 

 iris as the animals grow older. 



" In no case have I noticed any convergence of the eyes, or 

 any contraction of the pupil in accommodation for near objects. 

 Sudden bright illumination, however, invariably causes con- 

 traction. 



" The Cat's iris contracts in a very definite and curious way. 

 It may be imitated most accurately by causing two discs to 

 overlap, until the horizontal diameter is equal to half the ver- 

 tical (acute oval), when the contraction ceases in the vertical 

 direction, but continues horizontally until the sides meet, 

 forming two parallel vertical lines in close contact. At the 

 extremities of this vertical slit there are always two round pin- 

 holes, which are caused by the inability of the fibres of the iris 

 to come further together ; if examined with a strong magnify- 

 ing-glass, the radiating fibres of the iris are seen surrounding 

 these points. 



11 When I held a Cat's face so that the unobscured sun shone 

 directly on the centre of the pupil, and its image could be seen 

 on the cornea, I noticed the pupil immediately contract to the 

 above-mentioned vertical slit. So close was the contact between 

 the free margins of the iris that, so far as I could judge, no 

 light entered the eye except through the two pinholes. In 

 fact, I found I could hold a Cat with the lids held apart so 

 that the sun shone directly on to the pupils, without it showing 

 any sign of discomfort, nor did the animal trouble to use its 

 nictitating membrane. In this respect it had the advantage 

 over the big Felidce. with pupils that contract in a circular 

 manner, since a circular pupil can never contract completely 

 so long as it remains a circle," 



