184 Memoir upon the compound 



eye presents it of two diiFerent shades, as we see in the locusta 

 lilifnlia:. lastly, in certain species the tunic of tlie cornea pre- 

 sents stripes variouslv coloured, and traced with the greatest re- 

 gularity. These stripes are parallel in the ^rijla/s lineola : some 

 are of a idackish brown, and others of a yellov. ish gray, the clear 

 colour of which dips into that of the rest of the eye. It must 

 be remarked, that frequently these shades are effaced after death, 

 on account of the alterability of the tunic of the cornea. There 

 are even species in which the tunic of the cornea is as it were 

 marbled ; then it exhibits various shades in diflerent parts of the 

 eye. ^ 



As to the tunic of the smooth or simple eyes, it is seldom 

 black in the orthapterce, and its colours are always uniform in 

 the same eye ; although they are much variegated, when we 

 examine a great number of species. The most common colours 

 are white, red, or pale green. 



A great number of hemipierce also present the tunic of their 

 cornea of colours pretty much variegated ; but its brown or 

 rather black tints are much more common than in the ortho- 

 pterce. As we find among the latter, several hcmiplercB present 

 the tunic of the cornea of their smooth eyes, either whitish or 

 of the most agreeable red, as is observed in the common grass- 

 hopper. Lastly, it appears to me, that almost all the liemipteree 

 which live in water have the tunic of their cornea completely 

 black ; perhaps it is the same with all the coleoplercE which have 

 the same way of living. 



The lepidoplerce furnished with the finest colours have also 

 the tunic of the cornea of shades greatly variegated. Never- 

 theless, among all those which fly at sunset or during the night 

 only, we observe that the tunic of their cornea is generally black. 

 To conclude : the case is the same with several species of diurnal 

 butterflies: for instance, the papllio podalirivs has the tunic of 

 the cornea completely black ; and notwitlistanding the sombre 

 hue of this colour, the varnish of the choroid is very thick in 

 this species. In the papilio atalanla the tunic of the cornea 

 is of a clear brown ; thus the black point resulting from the- 

 aperture through which the optic nerve passes, is seen on the 

 outside of the eve. It must be observed, hov.-ever, that as this 

 circular aperture is formed in this species by vesicular tracheae, 

 and these tracheoe being a little separated from each other, 

 the blacd; point which is seen generally at the exterior of the 

 eye, seems surrounded by other black points, which present a 

 peculiar form, all having a smalkr extent than the central point. 

 In the papilio curdu'i, the tiinic of the cornea is of a brilliant 

 green, but much clearer in the lower part of the eye than in 

 the upper, on account of the luminous rays less easily reaching- 



them. 



