| Budget Amount *help |
¥3,800,000 (Direct Cost: ¥3,800,000)
Fiscal Year 2004: ¥800,000 (Direct Cost: ¥800,000)
Fiscal Year 2003: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 2002: ¥2,300,000 (Direct Cost: ¥2,300,000)
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| Research Abstract |
The eye of Ligia exotica is of the apposition type and has open rhabdoms. The facets are hexagonal, and the dioptric apparatus consist of a flat cornea and a spherical crystalline cone placed in the canter of two large cone cells. Each ommatidium has seven regular retinula cells and one eccentric cell ; basement membrane forms the proximal boundary of the retina. With increases in body size from 0.6 cm to almost 4.0 cm (or some are more), facet numbers and ommatidial diameters increased from 800 to 1500 and 35 μm to 100 μm, respectively ; eye length and width grew from 1.2 to 3.2 and 0.9 to 2.5 mm, respectively ; and length of dioptric apparatus and width of retinal layer changed from 70 μm to 180 μm and about 70 μm to 120 μm. Visual angles and interommatidial angles of centrally located ommatidia remained constant at about 30 and 6.9 degrees, respectively. An almost perfect linear relationship was found when eye length was plotted against the product between the square root of the tot
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al number of ommatidia and the ommatuaal diameter. No diference between males and females was observed in any of the relationships.
How does the number of the ommatidia increase? We tried to observe the marginal region of the compound eye of L. exotica. In order to characterize the marginal ommatidia from different eye regions, we made a detailed description of their distinct ultrastrtictural features in three different size-classes of Laxotica. On the bases of transverse as well as longitudinal sections we concluded that new ommatidia are added from a crescentic dorso-snterio-ventral edge of the eye and that maturing ommatidia go through a sequence in which originally the nuclei of cone-, pigment-, and retinula cells are arranged in three separate layers. At the beginning of the microvillar development, the organization of the corresponding rhabdomeres is still quite different from that of those rhabdomeres that make up the mature rhabdom. Marginal ommatidia always possess smaller diameters than more centrally located ones and retinal screening pigment granules are most apparent in the retinula cells only after the first micovilli have appeared.
In order to know the amount of the visual pigments following the increase of the number of ommatidia, we measured the amount of chromophores using the several different eye size-classes of Ligia by the oxime method. The smaller animals (smaller than 2cm in body size) possessed only 40 pmol, whereas, the larger ones (ca.3.5 cm) possessed 100 pmol in their two sessile eyes.
All of the value which we measure showed the increase following the increase of the body size, except the visual angle. Those results suggest that all specimens possess the same visual worlds basically because the larger specimens possess the almost same visual angles compared with the smaller ones. Less
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