Text-book of comparative anatomy . cerebral rudiment; these very often disappearthrough metamorphosis, or degenerate. As a detailed account ofthese always more or less complicated organs is here impossible, weselect a few for brief description, viz. the eyes in Capitella, in Alciope(the most highly developed eye among worms), in a Chietognathan, andin Hirudo. 1. The eye of Capitella.—The numerous eyes (ocelli) of Capitella liein the prostomium at the part where the brain fuses with the hypo-dermis. The following are theelements of a single eye. Wefind slipper-shaped refractingcells, whose oute
Text-book of comparative anatomy . cerebral rudiment; these very often disappearthrough metamorphosis, or degenerate. As a detailed account ofthese always more or less complicated organs is here impossible, weselect a few for brief description, viz. the eyes in Capitella, in Alciope(the most highly developed eye among worms), in a Chietognathan, andin Hirudo. 1. The eye of Capitella.—The numerous eyes (ocelli) of Capitella liein the prostomium at the part where the brain fuses with the hypo-dermis. The following are theelements of a single eye. Wefind slipper-shaped refractingcells, whose outer portion isand transparent,inner part containsEach of these cellsis continued as a nerve fibretowards the brain, this nervefibre entering a ganglion cell ofthe central optic lobe. Therefracting cells of the eyes areconnected together by threadcells of the hypodermis. Thecuticle is arched over theeye. 2. The eye of Alciope ().—The two eyes of Alciopestand out spherically, one onThey are covered by a thin layer of hypo-. homogeneouswhile thepigment. fl FIG. 153.—Section through the eye of an Alciope(Callizona Grubei). 7ij/, Hypodermis ; c, cornea ; 1,lens ; fl, eye fluid ; p, pigment of the retina ; r, retinalcells; st, rods; go, ganglion opticum of the brain(after Carriere). each side of the head. IV ORGANS 231 dermis with its cuticle, which form the outer cornea over the centreof the protruding eye. The eye itself is a vesicle whose posteriorthicker wall forms the retina, while the anterior thinner wall is theinner cornea. The elements of the retina are long cells standingclosely pressed together, in which three parts can be distinguished : (1)towards the brain, the cell body with a nucleus ; (2) the rod, which isdirected towards the hollow of the bulb; and (3), between these two,a thin layer of pigment. Under the cornea lies the spherical rest of the eye is filled with fluid. The retinal cells are continuedinto nerve fibres, which soon enter the ganglion
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectanatomycomparative
