414 JAMES ROLLIN SLONAKER 



pecten plays an important part in the process of acconnnodation 

 by changing the intra-ocular pressure, thus pushing the lens 

 forward. This view now has few supporters. Many try to 

 homologize this process in the bird with that in man and claim 

 that accommodation is due to changes in the shape of the lens. 



Hess ('13), in describing the process of accommodation in the 

 cormorant, speaks of the great change in the shape of the lens. 

 The anterior surface shows the greatest change. This bird has 

 a great range of accommodation, since it can pursue and catch 

 fish under water as well as see distinctly in the air. By the 

 use of nicotine he was able to harden the eyes and make sections 

 showing various conditions of accommodation, in which the 

 lens showed marked changes in shape. He claims that when 

 the eye is at rest it is accommodated for distant objects and the 

 lens is very much flattened; that when accommodated for near 

 vision the axial diameter of the lens is increased, making it more 

 spherical in shape. 



Beer ('93) claims that the contraction of Crampton's muscle, 

 because of its attachment to the inner lamella of the cornea, 

 exerts a pull on this part which results in a backward displace- 

 ment of the periphery of the cornea and an increase in curvature 

 of the anterior surface. This reduces the tension on the liga- 

 mentum pectinatum and allows the lens, from its elasticity, to 

 become more spherical. The increase in curvature of the lens 

 is especially noted on the anterior surface. This would be an 

 accommodation for near vision. When Crampton's muscle 

 relaxes the wall of the eye would assume its original passive posi- 

 tion, a strain would be put on the ligamentum pectinatum and 

 the lens would be flattened. This theory is a continuation of 

 that advanced by Exner ('82). 



A study of several hundred sections which I have of the lens 

 of the sparrow will not support this theory. If the lens changed 

 shape some of these numerous sections would show it. They 

 represent about fifty individuals killed at different times and 

 under various conditions. No change of curvature of the len- 

 ticular part of the lens can be noticed. The extremely firm len- 

 ticular part is so compact that when isolated in the fresh condi- 



