In this concentration of the rays we gain the first and by far the most important step towards the formation of a true, picture-forming eye; for we have only to place the naked extremity of the optic nerve, which in some of the lower animals lies deeply buried in the body, and in some near the surface, at the right distance from the concentrating apparatus, and an image will be formed on it.
Izpi-kontzentrazio honen bidez lehen pausoa, eta alde handiarekin inportanteena, egiten dugu benetako begia, irudi-formatzailea, eratzeko; izan ere, nerbio optikoaren mutur biluzia, behe-animalia batzuetan gorputz barruan sakonki gorderik eta beste batzuetan azaletik hurbil egoten dena, kontzentrazio-aparatutik distantzia egokira jartzea besterik ez daukagu, haren gainean irudia forma dadin.