. The microscope and its revelations. Fm. 731.—Head and compound eyesbee, showing the ocellile* in nitit on -idc, A, and displaced on the other, B •a, a, a, stemmata; b, b, ant<-nn;r. EYES 983 or squares; each facet is the corneule of a separate ocellite, and has a convexity of its own; hence, by counting the facets, we can ascertain the number of ocelli in each ; compound eye. In the two A eyes of the common fly there are as many as 4,000; in those of the cabbage-butterfly there are about 17,000; in thedragon-fly 24,000; and in the Mordella beetle 25,001). The structure of the arthropod ey
. The microscope and its revelations. Fm. 731.—Head and compound eyesbee, showing the ocellile* in nitit on -idc, A, and displaced on the other, B •a, a, a, stemmata; b, b, ant<-nn;r. EYES 983 or squares; each facet is the corneule of a separate ocellite, and has a convexity of its own; hence, by counting the facets, we can ascertain the number of ocelli in each ; compound eye. In the two A eyes of the common fly there are as many as 4,000; in those of the cabbage-butterfly there are about 17,000; in thedragon-fly 24,000; and in the Mordella beetle 25,001). The structure of the arthropod eye is best explained by a comparative account of the various stages of complication which it presents. In various larva? the cuticular layer is modified to form a single lens, behind which are simple, sepa- FIG. 732.—Diagram of a section of the. rate, elongated hypodermic cells,some of which are continuous withfine branches of the optic nerve;these may be called retinal next stage in complication isseen when last combine to formgroups, retinuhe ; the sensitivecells may become divided into tworegions, an outer one, which is vitreous and refractive in functi< in,while the inner part remains sensi-tive ; the corneal surface may In-come broken up into a number offacets, each of which corresponds toone of the pyramids so formed,and within the retinula there maybe differentiated a rhabdom (see ) formed by the nerve-rod. After traversing the pyramidsthe rays reach the extremities ofthe fibres of the optic nerve, whichare surrounded, like the pyramid,by pigmentary substance. Thus therays which have passed through theseveral corneules are preventedfrom mixing with each other; andno rays, save those which pass in composite eye of Melolontha vul-t/iiriij (cockchafer) : a, facets of thecornea; I, transparent py
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectmicrosc, bookyear1901
