Neuromag May 2017 - Page 23

Figure 2: Dolichpteryx longipes, a fish with a conventional tubular eye with refractive optics, and a diverticulum based on reflecting optics. A Dorsal view of a living specimen; the dotted line indicates the plane of sectioning of the following micrographs. B Thin section of the tubular eye and the diverticulum stained with methylene blue. C Diagram of the adjacent section: sclera-blue; choroid-black; retinal pigment epi- thelium-brown; rod inner and outer segments-green; remaining retinal layers-yellow; mirror-grey. D Visual field angles of the tubular and the diverticular eye. E&F Bright field and dark field micrograph of the diver- ticulum: Note the bright reflection of the mirror in dark field illumination with polarised light. G Schematic representation of ray tracing modelling demonstrating the function of the focussing mirror of the diverticulum (Fresnel principle) H&I High magnification bright field and dark field light micrographs of the mirror structure showing reflective crystals. J Electron micrograph of stacks of guanine crystals showing alternation of crystals and cytoplasm, each layer about 120nm wide, corresponding to the quarter wavelength of the incoming light and resulting in mirror-like reflection. of alternating layers (bioluminescence: 480 nm) of different optical densities is well known from other animals to act as a potent reflective device. In ad- dition, we recorded the orientations of these crystals along the length of the mirror and observed that they started almost parallel to the septum ventral- ly, and then increasingly changed the orientation more dorsally. Modelling these data demonstrated that the in- coming light from below was thus ef- fectively reflected and focussed at the outer limiting membrane level, i.e. the rod outer segment acceptance open- ing of the lateral retina (Fig 2G). By adding such a downward-facing diver- ticulum to its tubular eye, therefore, Dolichopteryx almost doubles the range of its visual field (Fig 2D) and is capable of surveying the waters above and below. proctids compris R6WfVvVW&@7V6W3vWfW"FRF֖0&VF62&Rf"g&6WGFVBbFW6RfRGV'V"WW2vFFfW"ЧF7Vbf&W26W2BFVw&VW2`6WFW2Gvf֖ƖW27FЧ&7GW2frBvFW&fRF琦WG6WFw2FRWbF&VP7V"W'2R66W&6&B@&WFvFVvVFVBfVG&ЦFW&( vF~( F֗GFrƖvBFFfW'F7V"&WFFB62&FW&VB֗'&"ƖR7'7F2vRfR&VV&fVvVBF&RFRf'7@F&W'BF2֗'&"&6VBf7W76pFWf6RFRFfW'F7VVbFRFƒЦ6FW'WRF6'&vVV@&VGvg&6WfW&'F&ЧG2BFW67&&VB''66fVBRbFRfVFW'2bFRL;&vVw&GVFRG&r6VG&RB%0f"WW&66V6R'WBWfW"&Vf&P'6W'fVBfW'FV'&FW2FW&W7Fvǒf7W76rV6W2vF6֖"FЦ6&6RvW&RFWfVVB'g&W6VFRF6VGW'f"V&ǐƖvFW6W2FRG&wVr'6W'fFW&R2F@'f7V6V2bFƖ6FW'FW67&&VBV&ƖW"FRFfW'F7VVЦ2fW'6֖"FF26R ( &֗Ff^( 6GVF7F&7W2गB2FVFrF7V7VFRFBF0֖vB&RFW"66RvW&RFrЦV&V6GVFW2vVgW'FW &'&VWR7V6W2&Fǖ622FfW'F7VV66FW&&ǒ&rЦW"FFRGv&WfW2f֖ƖW3vWfW"7FVBb7'7F֗'&"@W6W26&V6V7FfRF77VRV0Ff7W2ƖvBFFR&WFbFPFfW'F7VVfǒ&6W0&W6VG26GVFBf'7B6vBfW'6֖"FFR( ֗'&"W^( FfW'F7VVЦbFƖ6FW'vWfW"FR֗"Ч&"vFG2wVR7'7F2v6FƖ6FW'2FW&fVBg&FR&WFЦvVBWFVƗV&6ЦW22FRW'&F7FW2bFP6&B2W6Fr2W"F66fW'bFPFƖ6FW'֗'&"WRv2BFPFRBGW&VBWBF&RFRWFЦFW"7W'&6r7F'vVvRV@BFRWW2bFRFW"V&W'2`FR&'&VWRf֖ǒFR7FFW6R'6W'fF2VBFBV7@GvgW'FW"VW7F3vB267V6&WB&'&VWW0FBW2FVFRǒf֖ǒ`FVW6Vf6vFFFRFfPWffVB7V6f&WGbFffW&VBWPFW6v3@vB&RFRF֖2&VFЧ62vFFR7F&7FBf֖Ǔ6V&ǒ&R'v6FFvBV7FVBV7V"FF@&W'2&RVVFVBF6fRFW6PVW7F2B66RFW6R&WV&Pg&W6F77VRf"D"$Ǘ62&RFVW6V7'V6W2&RVB'Bg&FRW6FVVBbW"ЦrFRf66FrfVbFRFVWFRv&&W6V&66&fFW0Vf&vWGF&R66WW&V6S6&Fb&Bv&&&Bf7W76VBBvFWBFRF7G&7F0bFR"BR6WVBvFЧFV6RB&GV7FfRFW&7FvFg&VG2B6VwVW2&bG"2Ԧ6vvW v&2BFRVfW'6G`L;&vVFRFW'FVB`FגBV2֗p&F66VFf2F66fW'@F&6VVrGfVGW&RॳvvW"ԢFVv2"g&B&&W'G2rb'G&FvR2#fVfW'FV'&FRWRW6r&F&Vg&7FfRB&RЦfV7FfRF727W'&VB&wb@#rUU$r#0