558 THE SENSES AND SENSORY ORGANS. 



seeking of the infinite scarcely compatible -with the practical 

 needs of life. 



Yet it appears that Notthaft's conclusions are consistent with 

 Grenacher's theory of a minimal pencil of parallel rays only 

 acting upon a retina. 



If Notthaft's paper had been written to prove the untenable 

 character of M Oiler's hypothesis from an optical point of view, 

 it would be intelligible ; but if I understand it, Notthaft is 

 serious and believes that he has aided in proving its validity. 



That he had doubts in his own mind is clear, for he quotes 

 Bates, who asserts that it was long before he could distinguish 

 Humming-birds from the Humming-bird Hawk-moth, Macro- 

 -A'ssa titan ; and asks ' If it is possible that one of these little 

 creatures can see well and the other hardly at all ?' He care- 

 fully proves that insects see as well as birds, or appear to do 

 so ; and yet he apparently tries to convince himself of the truth 

 of his 'darkness hypothesis,' as he is satisfied that the compound 

 eye is constructed as Grenacher describes it, and that no other 

 hypothesis can explain its function on principles which are 

 optically possible. 



Effect of the Subcorneal Image. The existence of a subcorneal 

 image, in itself, renders Muller's theory completely untenable. 

 Since the conditions of vision under the theory are most perfect 

 for objects seen by pencils of parallel rays, and every lenticular 

 system which tends to render the rays of light either convergent 

 or divergent would render vision less distinct, and as the small 

 axial pencil only could be effective, since the power of this pencil 

 would be rendered less with every increase of convexity in the 

 lens, it is evident that the existence of a lens would be a dis- 

 advantage and not a benefit to the possessor of a compound eye. 



It has been suggested that the lens acts as a condenser, and 

 (MiiSL-s a larger pencil to act upon the nerve end organs ; but 

 it is evident that this could only be effected by an increase of 

 the angular aperture of the lens and a corresponding deficiency 

 in the acuity of vision, as it is only by collecting the light from 

 ;t Urge surface and condensing it upon a small focal point that 

 a condensing lens is effective. 



