54 BARKER : 



"An image formed by several thousand separate points, of which 

 each corresponds to a distinct field of vision in the external world, will 

 resemble a piece of mosaic work, and a better idea cannot be conceived 

 of the image of external objects which will be depicted on the retina of 

 beings endowed with such organs of vision than by comparing it with 

 perfect work of that kind." 



It appears that Miiller supposed the cones to be empty 

 tubes radially arranged, each with a minute aperture, resting 

 upon a retinal surface. If that were true and if the foci of 

 the corneules were always the same as the length of the cones, 

 then a strong probabilitj^ would be established ; but neither of 

 these things is true. 



However, his view was not seriously attacked until the 

 year 1852, when Gottsche disputed the mosaic theory on the 

 ground that each separate corneule gives a separate and dis- 

 tinct image ; and although this fact was not new, Leeuwen- 

 hoek and others having observed it, his statement made a 

 great impression upon all who were interested in the subject. 

 In the words of Dors, the theory of Miiller was " abandonne 

 par tout le monde." 



Gottsche was not merely a curious observer of the images 

 formed by the corneules. He had studied the whole structure 

 of the compound eye, and notwithstanding the presence of the 

 cones, which he knew as solid refracting bodies, he believed 

 that images were formed on a retinal surface. * 



* As the statements found in the best text l)ooks of a science may be 

 supposed to fairly represent the state of that science at the period of 

 publication, we quote the following from Orton, 1876 : " But the proper 

 visual organs of Lobsters, Crabs anil Insects are two compound eyes, 

 perched on pedestals, or fixed on the sides of the head. They consist of 

 an immense number of ocelli pressed together so that they take on angu- 

 lar forms — four-sided in Crustacea, six-sided in Insects. They form two 

 rounded protrubances, variously colored — white, yellow, red, green, 

 purple, brown, or black. Under the microscope the surface is seen to be 

 divided into a host of facets, each being an ocellus complete in itself. 

 Each cornea is convex on one side, and either convex or flat on the 

 other, so that it produces a focus like a lens. Behind the corne;i or lens 

 is the pigment having a minute aperture or ' pupil.' Next (in place of 



