The Evolution of Optics. 289 



able mysteries about them that puzzle me beyond measure : First, how 

 do they construct covered ways by the million whose engineering 

 difficulties and tremendous labor exceed those of the Mount Cenis 

 tunnel by man, with never a mining or building worker showing itself 

 to view ? How do they build from an incomplete tunnel-end without 

 exposure to light? Second, how do they, absolutely eyeless, know 

 darkness from day f Third, and most wonderful, why does the huge 

 queen, whose whole life is spent in one spot, in the dark, and in lay- 

 ing eggs, have eyes, and her progeny have none ? 



Lastly may be briefly noticed some of the ingenious ways by which 

 Life has outwitted darkness and made it possible for her children to 

 see in spite of denied or diminished light. These devices consist prin- 

 cipally of three classes : 



1. Widening of the iris, diaphragm, or window-curtain of the eye, so 

 to gather a larger quantity of weak light. Every child knows the re- 

 markable power of the cat to widen the pupil in darkness and narrow 

 it to a mere thread-like slit in the light. 



2. Increasing the size of the whole eye with the same object in view 

 and synchronous with the enlargement of the pupil also. 



3. The creation of the tapetum lucidum in nocturnal vertebrates, 

 such as the tiger family, dogs, etc. This, as Dr. Alleman has pointed 

 out, is an organic concave mirror usually about one third the size of 

 the retina, situated at the back part of the eye, and gathers to a focus 

 in front of the animal the little light that may enter the eye in the 

 dark. It is a structure too little studied and understood. One can not 

 comprehend how the same light can be used to stimulate the retina and 

 also be reflected out of the eye. This physical difficulty has always 

 made me wonder if the light it throws in front is not phosphorescent 

 or self -created. 



4. The development of the function of phosphorescence. No human 

 chemist or physicist has ever been able to understand how these nu- 

 merous animals can create light without at the same time creating a 

 burning heat. The Edison who does this for our street and house 

 illumination has awaiting him a fortune greater than that of Jay Gould 

 and Vanderbilt combined. We are some way behind the glow-worm 

 yet, despite the naturalists. 



5. Finally, the hypertrophy or refinement of the tactile and other 

 senses may in part compensate for the loss of sight. The antennae and 

 feelers of many insects are doubtless thus used. The acuteness of the 

 sense of touch of blind people is well known. Blind men have been 

 authorities in the science of conchology, in numismatics, in botany, 

 etc., and something akin to the distinctions of color are credited to 

 some blind people. The timbre of the sound of a struck object aids 



