昆虫单眼的结构和功能

大多数昆虫的视觉器官除了复眼外还有一些简单的小眼,称为单眼。昆虫成虫和半变态类若虫的单眼称为背单眼,位于头顶两复眼之间。背单眼在数目和结构上都有较大变化,但基本结构包括角膜晶体、一层角膜生成细胞(覆盖在角膜晶体上)、视网膜(由大约1000个感光细胞构成,视类群而不同)。背单眼对弱光比较敏感,但在图像感知方面的作用并不显著;它是一种“激发器官”,可以增加复眼的感知能力。全变态昆虫的幼虫既没有复眼也没有背单眼,但在其头部两侧有些类似复眼小眼的侧单眼。侧单眼的结构也与小眼相似,包括角膜,晶体和由一些视网膜细胞组成的视杆。侧单眼是完全变态类昆虫幼虫仅有的感光器官,与复眼一样,它们可以感知颜色、形状、距离等等。

The structure and function of simple eyes of insects

In addition to the compound eyes,most of the insects have some simple eyes called ocelli.Adult and nymphal hemimetabolous insects possess some simple eyes on the head between the compound eyes called dorsal ocelli.Dorsal ocelli vary a lot in number and in structure,it also vary somewhat,but typically it is made up of a corneal lens,a layer of corneagenous cells(which secrets the lens),and the retina(which is composed of up to 1000 photosensitive cells depending on the species).Dorsal ocelli have been shown to be low light sensitive,but are apparently not important in image perception.They may be “the stimulatory organs“ that increase the sensitivity of the compound eyes.Many larvae of holometabolous insects lack both compound eyes and dorsal ocelli,but they possess some simple ocellilike stemmata on each side of the head.The structure of the stemmata is similar to an individual ommatidium of compound eyes.Typically it consists of a cornea,a crystalline body and a number of retinal cells forming a rhabdom.Stemmata are the sole visual organs in holometabolous larvae.In various insects they have been shown to be involved with color,form and distance perception like compound eyes.