1894.] 



PUPILS OF THE PELID-E. 



483 



The only condition which appears to have an influence on 

 the shape of the pupil seems to be age. My observations 

 on the above-mentioned cats, and on a number of others, all 

 lead me to the conclusion that the 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 uo 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 contraction. 



The cat's iris contracts in a ver^'' definite and curious way. It 

 may be imitated most accurately by causing two discs to overlap, 

 so as to form the figures indicated in the diagrams shown above, 

 until the horizontal diameter is equal to half the vertical (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 (see tig. 3). At the extremities of 

 this vertical slit there are always two round pinholes, which are 

 caused by the inability of the fibres of the iris to come fiirther 

 together ; if examined with a strong magnifying-glass, the 

 radiating fibres of the iris are seen surrounding these points. 



Kg. 2. 



Fig. 3. 



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 sHt. 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 



