The Cambridge natural history . Fig. 93.—Pecten opercularis L., showing theocelli on the two edges of the Fig. 94.—Compound eyes {) of Area harhata L.; ,mantle fold ; omm, ommatidia. (After Patten.) the middle. These brown spots, or eyescompound, being made up of the fusion of a number of^ Berulerloch, p. 136. ^ Quart. Journ. Micr. Sac. xx. p. 443. 192 ORIGIN OF FUNCTIONAL EYES chap. ommatidia (from 10 to 80) into one large round eye, which isgenerally elevated above the surface of the surrounding epithe-lium. Sometimes these eyes themselves tend to fuse together. Inone specimen
The Cambridge natural history . Fig. 93.—Pecten opercularis L., showing theocelli on the two edges of the Fig. 94.—Compound eyes {) of Area harhata L.; ,mantle fold ; omm, ommatidia. (After Patten.) the middle. These brown spots, or eyescompound, being made up of the fusion of a number of^ Berulerloch, p. 136. ^ Quart. Journ. Micr. Sac. xx. p. 443. 192 ORIGIN OF FUNCTIONAL EYES chap. ommatidia (from 10 to 80) into one large round eye, which isgenerally elevated above the surface of the surrounding epithe-lium. Sometimes these eyes themselves tend to fuse together. Inone specimen of Area JVoae, 133 of these faceted eyes werecounted in one mantle border, and 102 in the other. There can be little doubt that the development of thesefunctional eyes, or sensitive spots, in bivalve Mollusca, is due tospecial needs. They appear to be entirely absent in fresh-waterbivalves (with the exception of Di^eissensia, which is obviously amarine genus recently become fresh-water), while they are mostabundant in genera living between tide marks (Solen, Mya,Mactra), and most highly specialised in a ge
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1895
