IMAGES THEOWN BY THE CORNEA. 165 



It must, moreover, be remembered that in our eyes 

 the whole field of vision is reversed, so that different 

 objects remain in the same relative position. In the 

 case of insects, however, it would be the image thrown 

 by each facet which would be reversed, and hence the 

 general effect would be altogether false. 



We must not attach too much importance to the 

 mere presence of an image. Any lens-like object, even 

 a globule of fat, will give one. Moreover, as Miiller 

 and Helmholtz have shown, the lenses of the cornea 

 would be an advantage on the theory of mosaic vision, 

 by assisting to condense the rays of light on the 

 termination of the nerve. 



Gottsche's observation was made on the eye of the 

 blow-fiy (Musca vomitoria), and, as a matter of fact, the 

 fly is one of those insects which do not possess a true 

 crystalline cone. It is, therefore, probable that the 

 image which he saw was that of the cornea. Moreover, 

 as is shown by his figure, which I give below (Fig. 113), 

 he states * that the image was formed at x, while the 

 retina is far away at y. He suggested, indeed, that 

 the so-called optic ganglion really corresponds with 

 the retina of our own eye ; but this would not remove 



* His words are — " An der liintern Flache der Crystallkorper im 

 Fliegouauge kehrt sich siclier das Bild um, well das Bild dera object 

 in der Lage gleich ist, und da das Mikroskop das Object einmal 

 umkehrt, so muss hier eine doppelte Umkehrung stattfinden, einmal 

 durcli das Mikroskop und voriier durch den paraboliscben Crystall- 

 korper. Entsteht nun bei x (Fig. 113) ein umgekehrtes Bild, so ist 

 die Fr.age, wird das ganze Bild von x durch den Stiel zur Retina 

 und zur Perception bei y hingeleitet oder wirkt dieser diinne Stiel 

 gleichsam wie ein Diaphragma und giebt er nur einen Theil des 

 Bildes bei x nach y '* (Gottsche, " Beit, zur Auat. und Phys. des Auges 

 der Krebse und Flicgeu," Arch, fiir Anat. Phys. und Wiss. Medicin.^ 

 1852). 



