. The Annals and magazine of natural history; zoology, botany, and geology. 234 Mr. F. E. Beddard on a his important memoir * on the Arthropod eye. The vitrellaf in both types consists of two cells, which secrete a round or pear-shaped crystalline cone ; this crystalline cone is evidently composed of two halves closely applied together, each half being formed from a single cell of the vitrella. The retinula in both types is seven-celled; each cell secretes a chitinous refracting rod—the rhabdomere ; these become fused into an axial structure—the rhabdom—in PorcelUo; in Gymothoa each rhabdomere
. The Annals and magazine of natural history; zoology, botany, and geology. 234 Mr. F. E. Beddard on a his important memoir * on the Arthropod eye. The vitrellaf in both types consists of two cells, which secrete a round or pear-shaped crystalline cone ; this crystalline cone is evidently composed of two halves closely applied together, each half being formed from a single cell of the vitrella. The retinula in both types is seven-celled; each cell secretes a chitinous refracting rod—the rhabdomere ; these become fused into an axial structure—the rhabdom—in PorcelUo; in Gymothoa each rhabdomere remains separate and within the retinula-cell of which it is a product. I have recently studied the structure of the eye in several species of ^ga and allied genera, and find some notable differences from the types already mentioned as well as from all other Isopods, excepting the genus Serolis. In Scrolls I the retinula differs from that of PorcelUo &c. in being composed of only four cells; each cell secretes at its upper extremity a chitinous rhabdomere : the rhabdo- meres are more or less completely fused together along their inner faces, but the rhabdom is not imbedded between the retinula-cells; on the contrary, each of these cells, owing to its peculiar shape, is only in con- tact with the upper part of the rhabdom; the lower j)ortion is sur- rounded hy two large spherical trans- j>arent cells, which Jit iji closely between the four retinula-cells (see woodcut). These cells are distinctly nucleated (h), the nucleus possessing a well-defined nucleolus. In sections it can be readily seen that the rhab- dom, which at its inferior extremity becomes divided into four separate pieces (corresponding of course to the four rhabdomeres of which it is composed), is imbedded in, or at least is entirely surrounded by, the substance of these large clear cells. * ' SeLorgan der Arthropoden/ Gottingen, 1879. t This term has been introduced by Profs. Lankester and Bourne (Qu
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