CHARTER IV. 

 ACCOMMODATION AND CONVERGENCE. 



Intimately associated with the evolution of the fovea 

 centralis, and therefore with the adoption of arboreal life, is 

 an increased capacity for accommodation and convergence. 



The accommodative power of the eyes of mammals has 

 been investigated by several different observers. All are 

 agreed that its range is greatest in man, slightly less in apes, 

 and very considerably less in all the lower orders. 



Hess and Heine 27 found its range equal to 10 to 12 I), in 

 apes; 2.5 to 3.5 I), in dogs; 1.25 I), in cats; 2.5 to 3 I). in a 

 young wolf; and in rabbits. 



Barrett 28 was unable to detect any alteration of refraction, 

 during examination by retinoscopy or with the ophthal- 

 moscope, in any mammal except man and monkeys. Those 

 which he examined were rabbits, guinea-pigs, rats, mice, 

 cows, horses and dogs among domestic animals; and deer, 

 jackal, pecari, various cats, hyena, opossum, porcupine, 

 mongoose and thirteen monkeys among wild animals. He 

 found that electrical stimulation of the eyes of cats and dogs 

 produced no result, and that the voluntary accommodation 

 of monkeys was equal to 4 to 5 I). 



Beer 29 estimated the range of accommodation in Macaeus 

 rhesus as equal to 10 I)., and that in the anthropoid and 

 some other apes it was still greater, approaching even in 

 the untailed apes to the degree present in man. By electrical 

 stimulation of the freshlv enucleated eve of the common cat 



