推荐回答(2个)
昆虫和甲壳动物的眼是别具一格。从外观上来说,它们头部是长着一对不小的眼,但仔细分析,其实每只眼是由几百只甚至成千上万只小眼组成,故特称为复眼。整个复眼呈半球状,每个小眼则呈锥状。如象鼻虫的复眼,如果在中部剖开一小部分,可以看到小眼一个挨一个地紧密地排列着。每只小眼朝外的一面有一层角质的晶状体,光线可以从此处透入,其他部分的表面是一层色素层,使光线不能穿过,从而使相邻的小眼相互隔开,成为功能上各自独立的小眼。复眼本身不会转动,动物是靠转动头部才使复眼朝向所要看的地方。经研究发现,在复眼注视某一目标时,通过小眼角膜晶体的折光系统,可同时在每个小眼形成一个物像。既然对于同一个目标,却由小眼形成许许多多相同的景象,人们不禁会问,这有什么必要?这不是“多此一举”吗?其实不然,它非但不是“多此一举”,相反,这一装置有着许多美妙功能,人类还要拜它为师呢。例如,有模仿蝇眼而研制出的“蝇眼”照相机,有模仿复眼测量运动的物体的速度的特别速度计等等。
复眼美妙功能之一,是提高时间分辨率。一件物体摆在眼前,人通常需要盯住物体观看0.05秒才能看清楚,但苍蝇或蜜蜂,只需约0.01秒就够了。螳螂从发现猎物到用带锯齿的前足捉住猎物,整个过程只需0.05秒就可完成。所以,有些一晃而过的物体,对人类来说根本未能看清,但具复眼的昆虫,可能已辨别出其形状大小了。上面提到的模拟蝇眼研制出的“蝇眼”照相机,它的镜头由1329块小透镜粘合而成,一次能拍摄出1329张照片,分辨率高达每厘米4000多条线条。这种照相机可以用来复制十分精细的显微电路,这些显徽电路在电子计算机中是广泛使用的。复眼的另一美妙功能,是它的高效测速功能,它可称得上是一精巧的测速计。如前所说的象鼻虫,它的复眼呈半球形,整个复眼的视野超过180°,就看东西的范围——“视野”来说,比人的要宽广得多。对一个在活动着的物体,如小虫子,复眼中的所有小眼,并不是同时看到它的,各个小眼是有先有后地看到这个物体的。反过来说,当具复眼的昆虫在空中飞舞时,对地上的花草等静止不动的物体,也不会像我们坐汽车、火车时看窗外的树木、电线杆那样,看到这些东西像在连续运动似的,而是看到一个个单个的景象。我们知道,放电影时,尽管电影画面是一幅幅的,但如果以每秒钟放映25幅的速度放映,那么那些动作不连续的画面,看起来会觉得是连续的。但如果让有复眼的昆虫去看电影,会是一幅幅不动的“定格”般的画面,若要它们感到是连续动作,每秒钟至少要放映几百个镜头才行。这对昆虫来说是很有好处的,因为在它快速飞行时,不会把各种不动的物体看成是连续活动的。不然的话,既发现不了要“着陆”的花朵,要捕食的猎物,也不能准确地发现敌人,有效地躲避敌人。由于昆虫飞行时,每个小眼都在观看它的视野范围内的景物,并获得它所观测到的“数据”,而根据这些数据,它们的脑就能“计算”出自身相对于地面物体的飞行速度,所以,在“着陆”时,能调整它的飞行运动,自动控制飞行速度,不快不慢,恰到好处地完美着陆。人们正是从中受到启发,于是模仿复眼的功能原理,研制出一种飞行器(如飞机、火箭等)对青蛙在伺机捕捉苍蝇时,从视觉上说,通过眼睛的影像,也许是一只颠倒的苍蝇地速度计。这种速度计是在飞行器上装备两个成一角度的光电接收器,而在地上一固定地点发出光学信号。由于两个光电接收器的位置是两者成某一角度(夹角)的,有如复眼中的某两个小眼,故它们必然是按顺序地接收地面上同一目标发来的光信号,因此,只要将两者接收到地面光信号的时间差,和飞行器的飞行高度,以及两个接收器所形成的夹角的度数等数据输入计算机,就能得出该飞行器相对于地面的相对速度,据此,就可以按要求来调整飞行器的飞行速度。
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