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distinguish objects at a sufficiently great distance, while others 
seem to possess the power of vision only for those which are 
very close. Finally, some of them are absolutely destitute of 
eyes altogether. 
We have already seen that the eyes of these animals are of 
two kinds, simple and compound. The former, which are 
sometimes called stemmata, are too small to be dissected in a 
satisfactory manner. 
As to the compound, or complex eyes, they are better 
known. We need hardly repeat that they are divided, like 
those of the insects, into a number of hexagonal facettes, 
slightly convex, and which form so many small particular 
cornese, whose substance is very transparent, and thicker at 
the middle than at the edges. M. de Blainville informs us 
that their internal surface in the Palinuri, which we may 
take as an example, is invested with a sort of black vascular 
membrane, which must be considered as a true choroid. In 
fact, it is evidently pierced in the middle of each little cornea, 
by a small orifice, which should be analogous to the pupil. 
From this orifice proceeds a small membranaceous produc- 
tion, in the form of an extremely short tube, which is applied 
on a corresponding nipple of a considerable, sub gelatinous 
translucid mass, and which is indubitably the analogue of 
the crystalline, or vitreous humour. M. de Blainville has been 
unable to ascertain whether this mass is divided into as many 
parts as there are small tubes, by the prolongation of their 
very transparent envelope. But he has clearly recognized that 
this mass of vitreous humour, convex on one side, and concave 
on the other, is applied on a thick ganglion, or enlargement 
of the extremity of the optic nerve, which ganglion appeared 
to him also to present at its surface, as many small alveoli, as 
there are small ocular tubes. 
M. Cuvier has not found in the eyes of Astacus all the 
details of organization which M. de Blainville states that he 
