| OCR Text |
Show 1890.] OF THE EYE IN ARCTURUS. 371 narrow peripheral band left which is clear. The whole vitreous body appears to be more or less granular and opaque. (5) Arcturus brunneus, F. E. Beddard. In this species the vitreous bodies or lenses of the ommatidia have the form which is illustrated in the drawing exhibited (Plate X X X I. fig. 13) ; their shape is usually that of a buffet with the convex outer surface and a straightish margin where the lens comes into actual or at any rate very near contact with the rhabdom. As a rule the lens is decidedly smaller. The rhabdom, on the other hand, is particularly large. (6) Arcturus glacialis, F. E. Beddard. The eye of this species calls for no lengthy description, the vitreous bodies have the same curious muffin-shape that they have in A. spinosus; the rhabdom is large, and the nuclei of the retinula-cells are placed below it. (7) Arcturus studeri, F. E. Beddard. This is the only shallow-water species besides A. furcatus and A. americanus that I have studied ; unfortunately in this case, as in that of A. americanus, I am dependent upon a single sketch which I made some years ago ; the preparations themselves are missing. This is particularly to be regretted, as A. studeri resembles in some particulars species that only occur in deep water. The vitreous bodies, however, are quite like those of A. furcatus in their perfect transparency and in their general shape. I am unable to give any details about the rhabdom ; it does not, however, seem to be particularly large ; the retinula-cells are unlike those of A. furcatus, and like those of A. spinosus and all the deep-sea species described in the present paper in that their nuclei are placed below the posterior extremity of the rhabdom. Whether there is much or little pigment I cannot say. The following table indicates the depths at which tbe various species described in the present paper were met with:- I. Arcturus furcatus. 7-127 fathoms (one specimen in 1675 fathoms). 2. Arcturus americanus. 55 fathoms. 3. Arcturus studeri. 25-127 fathoms. 4. Arcturus glacialis. 1675 fathoms. 5. Arcturus brunneus. 1600 fathoms. 6. Arcturus anna. 600 fathoms. 7. Arcturus cornutus. 500 fathoms. 8. Arcturus spinosus. 1375 fathoms. The first three species are therefore to be looked upon as shallow-water forms ; the remainder as true deep-sea species. |
