标题：伪瞳孔
简述
当我们看着一个有比较大的复眼的昆虫（如螳螂、蝗虫等）的眼睛时，会发现它的眼中居然有个黑色瞳孔！而且无论我们（观察者）怎样移动，那个瞳孔状的黑点总是对着我们，于是我们难免怀疑：怎么昆虫的复眼什么时候变得和人眼一样了吗？其实这并不是真的瞳孔，昆虫学上把它称为伪瞳孔（pseudopupil）。之所以会有伪瞳孔，是有很复杂的光学原因的。
重要的有关研究资料１（十分难得的资料！）
以下英文原文资料来自自一网上的pdf：在此要特别感谢与我分享资料的茧园同志！！源地址：http://web.neurobio.arizona.edu/gronenberg/nrsc581/eyedesign/visualacuity.pdf
该研究档案的简介：（这是英国科学家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.
伪瞳孔成因
下为才我要找的东西（这个解释我真的期待了好久好久啊！）
More recently, measurements of“德尔塔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 “德尔塔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, “德尔塔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.
就是说，我们看到螳螂等昆虫的眼睛总是有个瞳孔看着自己（那个黑点叫做pseudopupil，即“伪瞳孔”），完全是因为正对我们视界的复眼中视杆细胞吸收了我们视轴的光因而才呈黑色。因此我看到有些香港人的解释说“黑点是正对视野处眼底反光而呈出的自己（观察者）的样子”的解释应该是不准确的。
＊研究者此处还提到了一种可广泛用于测定小眼（ommatidium）数量的方法，称为“Delta-Phi”，我理解的意思就是“角的变化量”，只要用一种小光圈的显微镜对准复眼的某一处（根据我的摄影知识，小光圈意味着景深大），因此在该测定中可保证角膜与伪瞳孔同时被看见（我们所见到的伪瞳孔在角膜之下），由于实际上是视杆束及其周围色素的放大图像，因此我们用显微镜定位出的为瞳孔实际就是一个视杆细胞（按照我的昆虫学知识理解，这种“伪瞳孔定位法”应该是比较精确的，因为内小眼（inter-ommatidium）的夹角是非常细微的，找到了伪瞳孔的正对位置也就自然能确定是一个小眼了。利用这种仪器在复眼上一个一个地数出小眼，可要比我们国家某某生物奥赛培训班中讲的算面积再相除的土办法要科学得多！）……不过他们强调道，如果内小眼的角度发生急剧的变化，伪瞳孔就会变得“不对称”（我理解是“不好捉摸”的意思）。
至此，对于以螳螂为代表的昆虫眼睛的疑惑，我是相信以上英国科学家的解释的。他们的测量结果及理论表述都是很严谨的。
不同状况下的伪瞳孔
后报告中继续写道：
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).

这就是说（这如果我理有误敬请指出），昆虫在暗处也有伪瞳孔，只是由于其眼部构造上的一种“交错的偏振性纤维”遮挡了反射光（这个我的确是从未注意到过的，对我来说确是个新发现。）文中指出，用光照射昆虫头的底部，就能在相近的视杆束（小眼）末端（就是解剖学上最深处的尖端）看到发光，这种状态下“发光的伪瞳孔”叫做“逆式伪瞳孔（antidromic pseudopupil）”，可用与那种通常情况下不发光的伪瞳孔（这个称顺式伪瞳孔，英文orthodromic pseudopupil）相同的测量方法（上面我的翻译中已提到）来进行测定。
(以上内容只是原研究报告的一小部分，进一步翻译工作还有待补充。)
总之，昆虫的复眼就是复眼
我们观察者所见的“瞳孔”只是一种正对位置的小眼对光的吸收效应所致。