5616 x 3744 px | 47,5 x 31,7 cm | 18,7 x 12,5 inches | 300dpi
Informations supplémentaires:
Most spiders have four pairs of eyes on the top-front area of the cephalothorax, arranged in patterns that vary from one family to another. The pair at the front are of the type called pigment-cup ocelli ("little eyes"), which in most arthropods are only capable of detecting the direction from which light is coming, using the shadow cast by the walls of the cup. However the main eyes at the front of spiders' heads are pigment-cup ocelli that are capable of forming images. The other eyes are thought to be derived from the compound eyes of the ancestral chelicerates, but no longer have the separate facets typical of compound eyes. Unlike the main eyes, in many spiders these secondary eyes detect light reflected from a reflective tapetum, and wolf spiders can be spotted by torch light reflected from the tapeta. On the other hand jumping spiders' secondary eyes have no tapeta. Jumping spiders' visual acuity exceeds by a factor of ten that of dragonflies, which have by far the best vision among insects; in fact the human eye is only about five times sharper than a jumping spider's. They achieve this by a telephoto-like series of lenses, a four-layer retina and the ability to swivel their eyes and integrate images from different stages in the scan. The downside is that the scanning and integrating processes are relatively slow.
