PROCEEDINGS library 



NEW V 



OF THE „„_ , 



Delaware County Institute of Science o^*^^'^ 



Vol. V, No. 2 January, igio 



THEORIES AND FACTS OF ARTHROPODAE VISION. 



BY ALBERT S. BARKER. 



ILLUSTRATIONS FROM PREPARATIONS AND PHOTOMICROGRAPHS 

 BY THE AUTHOR. 



" Ouelqne rationelle que seinble une theorie celle-ci n'a jamais 

 qu'une faible valeur tant qu'elle n'a pas ete confirmee par des experi- 

 ences multiples et varices. " — F. Plateau. 



"When I removed the tunica cornea a little from the focus of the 

 microscope and placed a lighted candle at a short distance, so that the 

 light of it must pass through the tunica cornea, I then saw through it 

 the flame of the candle iiiverted, and not a single one, but some hun- 

 dreds of flames appeared to me, and these so distinctly (though wonder- 

 fully minute) that I could discern the motion of trembling in each of 

 them." — Antonius von Leeuwenhoek. 



The obserYation recorded in the lines above was made two 

 hundred years ago with what would now be termed a simple 

 microscope, the only type of microscope known at that early 

 period ; but it may be noted that as compound microscopes 

 had not then been iuYented and as the desire for higher 

 powers was as urgent as it is in our day, the capacity of the 

 simple microscope was pushed far bej'ond what we try to 

 attain now, and Leeuwenhoek had one giving a magnification 

 of 270 diameters, with which instrument, still in existence, 

 Harting was able to resolve the fourth group of Nobert's 

 test-plate. 



It is probable that Leeuwenhoek 's microscope was the ear- 



