FORM-SENSE 55 



moscopic changes, might be due to an absence of any one 

 of the three above-mentioned characteristic features at the 

 macula, so that the condition we describe as ''congenital 

 amblyopia'' might be brought about in different ways; we 

 have, however, definite anatomical evidence that in con- 

 nection with it the fovea is sometimes found to be absent. 



Seefelder? 6 recorded the absence of the fovea in a case 

 of congenital amblyopia and nystagmus associated with 

 aniridia. Its absence has also been noted in congenital 

 amblyopia accompanying albinism. Further investigations 

 as to the structure of the retina at the macula in connection 

 with congenital amblyopia is, I suggest, much to be desired. 



Monkeys, the class of mammals which first developed a 

 fovea, like birds, in whom a fovea is almost always present, 

 live an arboreal life. They, like birds, subsist on a diet of 

 fruit and insects, which has to be picked up, picked off or 

 picked out. This picking process requires considerable 

 concentration and sharpness of vision. In the case of birds 

 it is done with the bill, and in the case of monkevs with the 



f \/ 



fingers. 



Other mammals who have adopted the arboreal habit, 

 such as lemurs, some of the Insectivora and rodents, have 

 not developed a fovea, the reason probably being that they 

 make more use of their teeth and comparatively elongated 

 snouts for the picking up and preparation of their food 

 than the higher Primates, and therefore require less acute- 

 ness of vision for detail. 



The adoption by monkeys of feeding habits, intimately 

 associated with the use of the hands and the formation of 

 a central spot of acute form-sense, endowed them with the 

 capacity of picking up objects and examining them closely. 

 Such a capacity would tend to excite feelings of curiosity, 

 the marked development of which is one of the characteristics 



