. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. FIGURE 9. Magnified profiles of the distal part of photoreceptor cell, a: Stage I. b: Stage III. P: pigment cell, RM: photoreceptive membranes. Scale: to the development of photic responses. Although the ultrastructure of ocelli has been studied widely in differentiated larvae (Dilly, 1961, 1964; Barnes, 1971; Eakin and Kuda, 1971), the work of Barnes (1974) on "embryos" of Amaroucium constellation, a compound ascidian, was the only one that followed the differentiation of the ocellus. Our observations confirme
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. FIGURE 9. Magnified profiles of the distal part of photoreceptor cell, a: Stage I. b: Stage III. P: pigment cell, RM: photoreceptive membranes. Scale: to the development of photic responses. Although the ultrastructure of ocelli has been studied widely in differentiated larvae (Dilly, 1961, 1964; Barnes, 1971; Eakin and Kuda, 1971), the work of Barnes (1974) on "embryos" of Amaroucium constellation, a compound ascidian, was the only one that followed the differentiation of the ocellus. Our observations confirmed and extended those of Barnes by introducing morpho- metrical aspects. Differentiation of photoreceptive membranes and the pigment cell proceeds rapidly within 3 h. One and a half h after hatching (Stage III) the larvae become responsive to a shadow. Although we could not ascertain the number of newly recruited photoreceptor cells between Stage I and Stage III, the increase in surface area of the photoreceptive membrane as estimated by the number of lamellae from single cells (from to ) and their length (from to ^m) should account for the functional maturation of the presumptive photoreceptor cells. The negative phototaxis then appearing from Stage IV onward is accompanied by a more than two fold increase in the ratio of the pigmented area in the B-portion to that in A-portion, resulting in both of the lateral sides of the ocellar lumen becoming loaded with pigment granules. This pigment disposition may aid the photoreceptors in sensing the direction of the light source. The arrangement of lamellae perpendicular to the incident light coming through the lens system may also be advantageous for photosensitivity. Considering that ocelli of newly hatched larvae which are indifferent to light are already equipped with the three major components (a single pigment cell, photoreceptor cells and three lens cells) of the ocellus, maturation of the central nervous netw
Size: 2685px × 931px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
