Literary Notices. xliii 



the death of the excluded individuals. Natural selection differs from 

 most of the other forms of isolation in that, acting alone, it is not capa- 

 ble of producing divergent ox polytypic evolution, for the only way in 

 which isolation of any form can cause such evolution is by partition- 

 ing a given group into two or more groups, each of which is able to 

 survive as thus separated from the other, and so carry on the evolu- 

 tion in divergent lines. But the distinguishing peculiarity of natural 

 selection, considered as a form of isolation, is that it effects the isola- 

 tion by killing off all the individuals which it fails to isolate. 



These points are developed succinctly and with convincing force. 

 Perhaps the strongest line of evidence adduced is the fact that they 

 were elaborated quite independently by another naturalist. Indeed 

 the remarkable resemblance between the views of Mr. Romanes and 

 those of Mr. Gulick, developed almost simultaneously on the oppo- 

 site side of the earth, reminds one forcibly of the dramatic way in 

 which the doctrine of natural selection was simultaneously published 

 by Darwin and Wallace. c. j, h. 



Theories Of Upright Vision.' 



The question why we perceive objects in their actual position in 

 spite of the fact that the retinal image is inverted seems doubtless to a 

 dynamic psychologist, a very naive one, due to a very superficial con- 

 ception of the process of perception. Nevertheless it is a problem 

 which actually gives a great deal of trouble to experienced thinkers. 

 Two theories have been invented to explain why the image must be 

 inverted to produce the percept of the natural position and both imply 

 that this inversion is essential to the proper upright vision. The first 

 theory is that the sense of position is derived from the motions of the 

 eye balls in bringmg the image of the object into the fovea. "Upper" 

 or "lower" mean, accordingly, those directions which require an 

 upward or downward motion of the eye to bring the objects into the 

 field of clearest vision. The second theory is that the retina has a 



'George M. Stratton. Some Preliminary Experiments on Vision with- 

 out Inversion of the Retinal Image. Psych. Rev. Ill, 6. 



James H. Hyslop. Upright Vision. Psych. Rev. IV, 2. 



George M. Stratton. Upright Vision and the Retinal Image. Psych. 

 Rev. IV, 2. 



George M. Stratton. Vision without Inversion of the Retinal Image. 

 Ibid. IV, 4, 5. 



C. H. JuDD. Some Facts of Binocular Vision. Ibid. IV, 4. 



A. Cameron. The Imagery of One Early Made Blind. Ibid. IV, 4. 



