Fig. 1

Growth and morphology of the compound eyes of Parhyale. a Adult Parhyale with a dark pigmented compound eye typical of gammarid-like amphipods (photo credit: Vincent Moncorgé). b Scanning electron micrograph of the head of a Parhyale hatchling. The surface of the cuticle is smooth, with no distinctive structure in the region covering the eye (marked by a dashed line). c, c' Growth of the compound eye recorded in stage 26 and stage 28 embryos, a 7-day-old juvenile and an adult. Scale bars, 50 μm. d Growth of the compound eye during lifetime of Parhyale. The number of ommatidia per eye (top) and the length and the width of the eye (bottom) scale linearly with body length. The eyes of females and males show the same rate of growth with respect to body length. e Fluorescence image of a Parhyale compound eye, sectioned and stained with DAPI to reveal nuclei. The photoreceptor nuclei are concentrated at the base of the eye (NL), below the rhabdoms. Crystalline cones (CC) show strong autofluorescence. Scale bar, 20 μm. f Longitudinal semi-thin section through a Parhyale compound eye, stained with toluidine blue. The crystalline cone of each ommatidium (stained dark blue, CC) and the underlying rhabdom (stained light blue, R) are clearly visible, surrounded by dark pigment granules. The nuclei of the photoreceptor cells are located below the rhabdoms (NL). The inset photo shows a section through the crystalline cone, which consists of two cells. Scale bar, 20 μm. g Illustration of acceptance and interommatidial angles measured from sections of adult Parhyale eyes. The acceptance angles of individual ommatidia are assessed from an optical nodal point in the middle of the crystalline cone and an assumed image plane located 1/3 of the distance down the rhabdoms (see the “Materials and Methods” section)