1S6 Memoir upon the compound 



If the tunic of the cornea presents shades much varied in tlie 

 lepidopterce and lutirtpterce, these shades are not less varied in 

 the liyniejiopteio', in wiiich we sometimes see a g^ay, a green, a 

 yellow, and even all the shades of black. C'ertain bees, and 

 particularly the violacea, present this tunic of the most opaque 

 black. Generally the liymenoplcrce have their cornea very thick, 

 and it is not diihcult to remove it bv thin slices. Someiimes 

 this cornea is surrounded by hairs, and rarely do they issue from 

 the cornea itself. In a great number of species, the circular 

 trachea is totally wanting; but its place is alwa\s supplied by 

 other- and smaller tracheae which surround the optic nerve, and 

 in general l!;ese tracheaj are extremely nmltiplicd. 



What has been said with respect to the eyes of the hymcno- 

 pterce is applicable to those of the (//p/er^, which have the tunic 

 of the cornea with the most variegated shades. In a certain 

 number of species these shades are very brilliant, and the ta- 

 lanus as well as the mvsca hold a distinguished j)art in this re- 

 spect. 



Certain specifes of syrpJms present, at the exterior of the eye, 

 two semi-circular stripes deeper than the general tint. These 

 stripes are produced as usual by a deeper shade of the tunic of 

 the cornea in this part of the eye: but what renders this disposi- 

 tion remarkalile is, that there are numerous hairs precisely in 

 this very part of the compound eye, and which originate from 

 the cornea itself. 



As to the eyes of the aptercp, they are in general of dark co- 

 lours, and not very large. These insects seem therefore not to 

 be much favoured in respect to the organ of sight, and probably 

 their way of life does not require acute vision. 



It is remarkable that the insects which live in water have in 

 general their eyes dim and opaque externally, nearly like those 

 which exist in dark place.?. Thus the nymphs of the LihelbdcB 

 in passing to the condition of a perfect insect assume brilliant 

 and transparent eyes, whereas previous to their last metamor- 

 phosis these eyes were dull and without lustre. This observation 

 has not escaped the sagacity of Reaumur in his History of In- 

 sects. 



In the descriptions which we have given of the situation and 

 form of the compound and simple eyes of insects, it will be re- 

 marked that the former disposition is less subject to vary than 

 the latter. This consideration might have arisen a priori, since 

 no form ran exhibit differences in any order of animals, without 

 other variations following in the parts which surround those 

 whose disposition changes. The only very remarkable example 

 which we can mention of the variation in the position of the 



compound 



