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Fig. 8. Geometrical interpretations of sample bases. (A) Geometry of standing and
lying hexagonal arrays. (B) Hypothetical organization of sampling units in
three neighboring eyelets. The retina of one eyelet has up to four sampling
units in the horizontal plane, subsuming a total of about 30–35°.
The smaller sampling base around 10° occurs within an eyelet, for instance
between units 1–2, 2–3, 3–4 in the middle eyelet. One
possibility for the larger sample base around 20° is that neighboring
eyelets span, for instance between units 1–1, 2–2, etc. (C)
Irregularities in the organization of eyelets indicated by the number of
nearest neighbors for several specific eyelets. (D) A horizontal section of
X. peckii illustrates an alternative explanation for the larger
sample base, connecting only nearest optical neighbors. The angles of two such
connections are indicated. Variation results because some eyelets lie in the
same horizontal plane as their neighbors, such as those in which the same
number of sampling units are visible (their optical axes in 2D indicated with
straight lines), while other neighbors lie outside the horizontal plane, such
as those in which different numbers of units are visible. Scale bars, 50
µm.
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