簡述
當我們看著一個有比較大的複眼的昆蟲（如螳螂、蝗蟲等）的眼睛時，會發現它的眼中居然有個黑色瞳孔！而且無論我們（觀察者）怎樣移動，那個瞳孔狀的黑點總是對著我們，於是我們難免懷疑：怎么昆蟲的複眼什麼時候變得和人眼一樣了嗎？其實這並不是真的瞳孔，昆蟲學上把它稱為偽瞳孔（pseudopupil）。之所以會有偽瞳孔，是有很複雜的光學原因的。
重要的有關研究資料１（十分難得的資料！）
以下英文原文資料來自自一網上的pdf：在此要特別感謝與我分享資料的繭園同志！！源地址：http://web.neurobio.arizona.edu/gronenberg/nrsc581/eyedesign/visualacuity.pdf
該研究檔案的簡介：（這是英國科學家１９９７年的研究成果）
Annu. Rev. Entomol. 1997. 42:147–77
Copyright
c 1997 by Annual Reviews Inc. All rights reserved
VISUAL ACUITY IN INSECTS
Michael F. Land
Sussex Centre for Neuroscience, School of Biological Sciences, University of Sussex,
Brighton BN1 9QG, United Kingdom
KEY WORDS: vision, eye, optics, acute zone, interommatidial angle
ABSTRACT
The acuity of compound eyes is determined by interommatidial angles, optical
quality, and rhabdom dimensions. It is also affected by light levels and speed
of movement. In insects, interommatidial angles vary from tens of degrees in
Apterygota, to as little as 0:24 in dragonflies. Resolution better than this is not
attainable in compound eyes of realistic size. The smaller the interommatidial
angle the greater the distance at which objects—prey, predators, or foliage—
can be resolved. Insects with different lifestyles have contrasting patterns of
interommatidial angle distribution, related to forward flight, capture on the wing,
and predation on horizontal surfaces.
偽瞳孔成因
下為才我要找的東西（這個解釋我真的期待了好久好久啊！）
More recently, measurements of“德爾塔phi” have involved the use of the pseudopupil
in its various forms. The pseudopupil, typically a black dot that appears to move
around the insect’s eye as the observer’s viewpoint changes, marks the ommatidia
that image—and absorb light from—the observer. Thus a line joining the
pseudopupil to the observer’s eye is the direction of view of the ommatidia in
that region. Local measurements of “德爾塔phi” can be made easily by rotating the eye
through a known small angle (a) and counting the number of ommatidia (b)
crossed by the pseudopupil, “德爾塔phi” is then a=b. Typically, measurements are made
with the animal centered on a goniometric stage, and the pseudopupil is observed
or photographed through a microscope (23). Where the interommatidial
angles are small, as for example in the acute zones of dragonfly eyes, the best
pseudopupil image lies some distance below the cornea (the deep pseudopupil),
and it is important to use a small microscope aperture so that both cornea and
pseudopupil can be visualized together. Because the pseudopupil is actually
a magnified image of both the rhabdom and its surrounding pigment, its center
must be located to find the ommatidial axis direction. Usually this is not
a problem, but where interommatidial angles change rapidly, the pseudopupil
becomes asymmetric and care is required.
就是說，我們看到螳螂等昆蟲的眼睛總是有個瞳孔看著自己（那個黑點叫做pseudopupil，即“偽瞳孔”），完全是因為正對我們視界的複眼中視桿細胞吸收了我們視軸的光因而才呈黑色。因此我看到有些香港人的解釋說“黑點是正對視野處眼底反光而呈出的自己（觀察者）的樣子”的解釋應該是不準確的。
＊研究者此處還提到了一種可廣泛用於測定小眼（ommatidium）數量的方法，稱為“Delta-Phi”，我理解的意思就是“角的變化量”，只要用一種小光圈的顯微鏡對準複眼的某一處（根據我的攝影知識，小光圈意味著景深大），因此在該測定中可保證角膜與偽瞳孔同時被看見（我們所見到的偽瞳孔在角膜之下），由於實際上是視桿束及其周圍色素的放大圖像，因此我們用顯微鏡定位出的為瞳孔實際就是一個視桿細胞（按照我的昆蟲學知識理解，這種“偽瞳孔定位法”應該是比較精確的，因為內小眼（inter-ommatidium）的夾角是非常細微的，找到了偽瞳孔的正對位置也就自然能確定是一個小眼了。利用這種儀器在複眼上一個一個地數出小眼，可要比我們國家某某生物奧賽培訓班中講的算面積再相除的土辦法要科學得多！）……不過他們強調道，如果內小眼的角度發生急劇的變化，偽瞳孔就會變得“不對稱”（我理解是“不好捉摸”的意思）。
至此，對於以螳螂為代表的昆蟲眼睛的疑惑，我是相信以上英國科學家的解釋的。他們的測量結果及理論表述都是很嚴謹的。
不同狀況下的偽瞳孔
後報告中繼續寫道：
In dark colored eyes the pseudopupil is often not apparent. Crossed polarizing
fibers can be used to cut down reflections, but a more generally useful technique
is known as the antidromic pseudopupil (15). Here the center of the head is
illuminated from below, and light finding its way into the proximal part of
the rhabdom(ere)s is emitted from their distal tips. This produces a luminous
pseudopupil, which can be examined in the sameway as the dark “orthodromic”
kind. Pseudopupil methods are discussed and reviewed in references (14, 23,
76, 87).
這就是說（這如果我理有誤敬請指出），昆蟲在暗處也有偽瞳孔，只是由於其眼部構造上的一種“交錯的偏振性纖維”遮擋了反射光（這個我的確是從未注意到過的，對我來說確是個新發現。）文中指出，用光照射昆蟲頭的底部，就能在相近的視桿束（小眼）末端（就是解剖學上最深處的尖端）看到發光，這種狀態下“發光的偽瞳孔”叫做“逆式偽瞳孔（antidromic pseudopupil）”，可用與那種通常情況下不發光的偽瞳孔（這個稱順式偽瞳孔，英文orthodromic pseudopupil）相同的測量方法（上面我的翻譯中已提到）來進行測定。
(以上內容只是原研究報告的一小部分，進一步翻譯工作還有待補充。)
總之，昆蟲的複眼就是複眼
我們觀察者所見的“瞳孔”只是一種正對位置的小眼對光的吸收效應所致。
