Pebruaky 25, 1898.] 



SCIENCE. 



269 



acquisition of knowledge of the past and 

 new arrangements and adaptations to meet 

 the requirements of a more exacting en- 

 vironment. The latent cells become func- 

 tional, and new associational paths are 

 formed which become, or may become, by 

 the law of habit, just as fixed and, onto- 

 genetically considered, as reflex, and organic 

 as the most definite inherited reflex action 

 and instinct. 



Some such theory as the above seems to 

 be necessary to explain the wonderful ad- 

 vance of modern civilization. It is cer- 

 tainly not explained by any one or all of 

 the three processes mentioned above, 

 namely, those of organic, intra-organic 

 and germinal selection. It may however 

 be considered as a continuation of the same 

 fundamental process. If the organism 

 were forced to evolve within itself, by the 

 slow process of organic selection, all the 

 adaptations necessary for such a civiliza- 

 tion as we have to-day, it is obvious that 

 after millions of years it would finally pro- 

 duce a world-colossus, or impossible gigantic 

 monstrosity. 



Arthur Allin. 



University of Colorado. 



BINOCULAR FACTORS IN MONOCULAR VISION. 



All experiments in monocular vision 

 have to be made with one eye closed or 

 covered. Some writers have maintained 

 that binocular factors are by no means 

 eliminated under these circumstances, but 

 that the movements of the closed eye yield 

 just the same sensation data as would re- 

 sult if the eye were opened. The following 

 observations may aid in the solution of this 

 problem. 



If an observer closes one eye and looks 

 steadily at an object situated in the median 

 plane and at about the same elevation as his 

 eyes, and then suddenly opens the eye that 

 was closed, he will note an appearance of 

 unrest in the object. Careful observation 



will show that the object seems to shift 

 horizontally in the direction of the eye that 

 was not closed. The shifting in apparent 

 position becomes very noticeable when the 

 eyes are alternately closed. The object 

 will seem to move backward and forward 

 in a horizontal line, always moving toward 

 the eye that has just been closed. If the 

 object is somewhat above the elevation of 

 the eye there will be a vertical movement 

 downward in addition to the horizontal. 

 This apparent change in position may be 

 observed best when looking at distant ob- 

 jects ; the stars and moon show it very 

 clearly. It is evident from these facts that 

 the closed eye is not converged toward the 

 same point as the open eye. At the mo- 

 ment of opening the eye there are double 

 images, and these double images are crossed 

 as is shown by the direction in which the 

 object seems to shift. In fact, it is fre- 

 quently possible to see the double images, 

 and to note that the one which appears 

 when the eye is open is on the opposite side 

 from that eye, that is, crossed. The crossed 

 images indicate that the closed eye is con- 

 verged beyond the object. When looking 

 at the stars or moon, however, in order to 

 have crossed double images the eyes must 

 be diverged, and the distance which ap- 

 pears between the images makes it evident 

 that the divergence is considerably beyond 

 the position of parallelism. 



Helmholtz* and Le Contef have both ob- 

 served that when the muscles of the eyes 

 are relaxed in drowsiness there is a ten- 

 dency for double images, which indicates di- 

 vergence of the axes, to appear. Le Conte 

 has expressly noted that the degree of di- 

 vergence is so great that the axes must be 

 considerably beyond the parallel position. 

 Evidently the facts observed when one eye 

 is closed are related to those which appear 

 in drowsiness. The closed eye tends to 



* Physiol. Optik 2" Aufl., p. 633. 



fAmer. Jour, of So. and Arts (3), ix., p. 160. 



