By assuming that each microvillus is a cylinder, the collective membrane area of the microvilli contained in the unit volume of the rhabdomere (Sv) was calculated as
The distal (vitreal) end of the outer segment elongates to form a process (the apical process) that bears 2 sets of microvilli, making up 2 opposite rhabdomeres. The inner segment contains a nucleus and sends out an axon from the proximal (sclerad) end toward the optic lobe.
saltator, like some other amphipods, possesses an undifferentiated cornea, a fused-type rhabdom attached to the crystalline cone, and five retinula cells in each ommatidium (Ball, 1977; Meyer-Rochow, 1978; Hallberg et al., 1980; Mayrat, 1981), including one small cell producing a rhabdomere and four other larger retinula cells (Ercolini, 1964).
The rhabdomeres are fused to each other to form a fused type of rhabdom that is observed in transverse section (Fig.
The retinas of principal eyes are everted, which is to say that the light-sensitive rhabdomeres
of their photoreceptors face toward incoming light, with the cell bodies positioned below (Fig.
(1993), they also share a V-pattern in the rhabdomeres
of the ommatidia, further supporting their relationship (Fischer et al.
The number of visual cells (rhabdomeres) within the retina determines the quality of image resolution (Foelix 1982).
Sensitivity.--Sensitivity (f-number), or the eye's ability to admit light, was calculated using values for focal length (F) and the diameter of the retina (d), measured from the extremities of the rhabdomeres in each species (Opell & Ware 1987).
exotica, because rhabdomeres
are frequently skewed and the axes of ommatidial groups of retinula cells are not always parallel to the axes of the dioptric structures.
moschata shows packed arrays of photoreceptor cells with microvilli, reminiscent of rhabdomeres, but without dioptric apparatus (Nishioka et al., 1962), together with an epistellar nerve running into the stellate ganglion (Young, 1936; Perrelet and Mauro, 1972).
The epistellar body of Octopus vulgaris was later re-investigated in detail using electron microscopy and found to contain cells that have microvilli very like those found in the rhabdomeres of the extraocular photoreceptors seen in other molluscs and arthropods (Nishioka et al., 1962).
The geometrical, interleaved arrangement of microvilli from the rhabdomeres
of individual photoreceptors in Palaemonetes [ILLUSTRATION FOR FIGURE 8B, C OMITTED] is replaced by a much larger, but less geometrical rhabdom in Rimicaris sp.