The Cambridge natural history . shell gapes (Fig. 93). In Pecten opercularis,jacohaeus, and maximus their number varies from 80 to Si^ondylus gaederoipus, a very inequivalve shell, 60 have beencounted on the right or fixed valve, and 90 on the left or uppervalve. Each ocellus is con- nected, by means of itsoptic nerve, with the largecircumpalleal nerve, and sowith the branchial gan-glion. They possess a cornea,lens, choroidea, and opticnerve, and, according toHickson,^ bear a consider-able resemblance to the vertebrate type of eye. In spite of this,the power of vision in these genera do
The Cambridge natural history . shell gapes (Fig. 93). In Pecten opercularis,jacohaeus, and maximus their number varies from 80 to Si^ondylus gaederoipus, a very inequivalve shell, 60 have beencounted on the right or fixed valve, and 90 on the left or uppervalve. Each ocellus is con- nected, by means of itsoptic nerve, with the largecircumpalleal nerve, and sowith the branchial gan-glion. They possess a cornea,lens, choroidea, and opticnerve, and, according toHickson,^ bear a consider-able resemblance to the vertebrate type of eye. In spite of this,the power of vision in these genera does not appear at all superiorto that of other Pelecypoda. According to the elaborate investigations of Patten, the eyes in Area occur upon the middle or ophthalmic fold ofthe mantle-edge, which is thickened at the end to admit of their reception. Alongthis is ranged a rowof dark brown spotsof various sizes,wliich are larger atthe anterior andposterior ends of themantle - edge, butsmaller and morenumerous towardsare many of them. Fig. 93.—Pecten opercularis L., showing theocelli on the two edges of the mantle.
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1895
