. A textbook of invertebrate morphology [microform]. Invertebrates; Morphology (Animals); Invertébrés; Morphologie (Animaux). 836 INVERTEBRATE MORPHOLOOT. ment unusual for Invertebrates. The extremity of the pro- cess is occupied by a number of clear transparent cells which serve as a cornea {co) and which are continuous with a zone of pigmented cells (pgf) analogous to an iris, and which pass grad- ually over into ordinary ectodermal cells. Upon the inner surface of the cornea is a mass of transparent cells constitut- ing a lens (Z), and below this lies the sensory portion of the eye. The opt
. A textbook of invertebrate morphology [microform]. Invertebrates; Morphology (Animals); Invertébrés; Morphologie (Animaux). 836 INVERTEBRATE MORPHOLOOT. ment unusual for Invertebrates. The extremity of the pro- cess is occupied by a number of clear transparent cells which serve as a cornea {co) and which are continuous with a zone of pigmented cells (pgf) analogous to an iris, and which pass grad- ually over into ordinary ectodermal cells. Upon the inner surface of the cornea is a mass of transparent cells constitut- ing a lens (Z), and below this lies the sensory portion of the eye. The optic nerve as it comes towards the eye branches; 1 CO ''~~. !,W""' Pig. 150.—Eye of Pecten (modified siiKhtiy from Pattbn). CO = cornea. op, op' = optic nerve. I = lens. pg - pigment-cells. la = blood-lacuna. rt = retina. U = tapetum luciilum. one branch (op'), passing to one side of the eye, bends inwards towards the axis of the eye between the retina-cells (rt) aud the lens. The sensory portion of the eye consequently is in- verted, the retina-cells being turned away from the light which must pass through the fibres of the optic nerve to reach them. Below the retina and separated from it by a space is a layer of tissue, the Capelum Imidum {il), which serves as a reflector and gives the metallic lustre which is characteristic of the. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original McMurrich, J. Playfair (James Playfair), 1859-1939. New York : H. Holt
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