the Compound Eyes of Insects. 208 
deny. In Sphinx Atropos, however, I first observed how the 
fibres of the optic nerve surround the apex of the conical 
lenses. like a cup, and pass forwards over the lens to its an- 
terior facet and to the cornea. ‘The nerve, therefore, forms a 
true retina which surrounds the crystalline lens like a capsule. 
The nervous fibril is readily broken off under the apex of the 
cone, but the retina is also always perceptible at this part. 
The reason why this has been overlooked appears to me to 
be that they used too weak magnifiers; with a magnifying 
power of 300 times my statements will be confirmed. I have 
often repeated the observations on Beetles, (for example, on 
Melolontha,) on Papiliones, (for example, on Pap. Urtice,) 
and others. Whether the crystalline lenses are cylindrical or 
hexagonal is difficult to say; and even where they may be 
6-angular, as in Melolontha, of which I am still doubtful, the 
angles must be much rounded. In Mel. vulgaris (Plate IT. fic. 
3.), and more distinctlyin Mel. Fullo (fig. 5.) veachlens appeared 
to me to consist of six three-sided prisms, whose bases are di- 
rected outwards, so that they with their apices rejoin one an- 
other convergent in the axis of the lens. Ata is the Jens, 
inclosed by the sheath of its retina and entire, at bisected ; 
two prisms cover the third, which lies under them. c is a 
single prism from the side; d a similar one seen from the 
side opposite to the basis, (fig. 4. of Sphinx Atropos). 
If this statement be true, the eyes of insects will appear 
only single ones inwardly aggregated; behind each cornea lies 
a crystalline lens with retina and choroidea; the layer of pig- 
mentum takes the place of the latter. The rays of the axis, 
therefore, would not alone, as Muller supposes, fall on the 
nerves, nor the other rays be absorbed by the pigment, but 
would fall on the retina exactly as in the human eye. I have 
not yet examined the construction in the pyriform crystalline 
Jenses without the cornea subdivided into facets. 
We thus discover every day a greater complexity of ap- 
parently simple organs, and a closer analogy with the human 
construction, even in the Invertebrated animals. I think I find 
a greater perfection in the organization of the eyes in the An- 
nelida, particularly in Hirudo, for instance. See my Lehrbuch 
der Vergleichende Anatomie, 2te Abtheilung, p. 428. 
[ Note.—Since these observations on the compound eyes of the Lepido- 
pterous Insects were published by Wagner, a similar structure has been 
detected by Burmeister in the compound eyes of some of the Branchiopo- 
dous Crustacea.—Ep1r- | 
Z2 
