188 THE MINUTE ANATOMISTS 



though it may superficially resemble an iris in being 

 pigmented, has no pupil, and absorbs almost all the light 

 which enters it. The humours of the vertebrate eye, 

 which Hooke thought he had found in the compound 

 eye, are not really to be recognised therein. Swammer- 

 dam derides certain naturalists, to whom he had demon- 

 strated the facets of the bee's eye (Leeuwenhoek is no 

 doubt one of these), and who had found in their hexa- 

 gonal form a reason why the cells of the honeycomb 

 should be hexagonal. On the same principle, says 

 Swammerdam, mankind with their circular pupils ought 

 always to make circular dwellings ! Among other 

 details he notes the fine branching air-tubes which run 

 between the elements of an insect's eye — a striking 

 proof of the goodness of his microscopes and the close- 

 ness of his observation. How can insects see with their 

 compound eyes ? Swammerdam answers that there is 

 no image formed upon a retina, as in the vertebrate eye ; 

 there is no regulated aperture for the admission of light ; 

 in short, the compound eye is not in any respect such a 

 camera obscura as the human eye. The luminous rays 

 must strike direct upon the cones, and there produce 

 sensations. He goes on to say that the vision of insects 

 is thereby rendered more acute ; it is because they 

 possess compound eyes that bees can see in the dark, 

 and that dragon-flies can take their prey on the wing. 

 But here Swammerdam places himself among those 

 "ingenious and hasty philosophers" who explain what 

 they do not really understand. Vision by means of a 

 compound eye was first made in some degree intelligible 

 by Johannes Miiller a hundred and fifty years after the 

 date of Swammerdam's account of the hive-bee. 



The sting, he tells us, is straight in the worker, curved 

 in the queen, and wanting in the drone. Though con- 



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