. Bulletin - United States National Museum. Science. Fig. 19.—Cyclosalpa virgula, aggregated form, a sagittal section of the ganglion and dorsal eye. From Metcalf and Johnson (1905). the eye is divided into two main portions; a basal portion (e') in which the rod-cells are dorsal to the pigment, and a terminal portion (e") in which the rod cells are ventral to the pigment. A little behind the mid-dorsal point of this eye there is an area of thickened pigment partially surround- ing a group of larger cells which are the remnant of the optic plug {e'", see also fig. 20) which in Cyclos
. Bulletin - United States National Museum. Science. Fig. 19.—Cyclosalpa virgula, aggregated form, a sagittal section of the ganglion and dorsal eye. From Metcalf and Johnson (1905). the eye is divided into two main portions; a basal portion (e') in which the rod-cells are dorsal to the pigment, and a terminal portion (e") in which the rod cells are ventral to the pigment. A little behind the mid-dorsal point of this eye there is an area of thickened pigment partially surround- ing a group of larger cells which are the remnant of the optic plug {e'", see also fig. 20) which in Cyclosalpa pinnata and •4- IJ'f'-fN'^fAM C. affinis is much better developed. In lMi7\\Am^:^%B!^^ and C. bakeri the optic plug becomes more closely united to the apical portion of the eye. In C. virgula there is but a vestige of this structure. Tho vestigial condition of its optic plug shows that, in the character of its large dorsal eye, C. virgula is intermediate between the more archaic Cyclosalpas on the one hand and the Apsteinias, Salpas, and other subgenera on the other. The optic nerve enters the eye passing above the basal rod cells (fig. 19).. Fio. 20.—Cyclosalpa virgula, aggre gated form, the middle portion of the section of the dorsal eye SHOWN IN FIG. 19, MORE niGHLY MAG- NIFIED. From Metcalf and Johnson (1905).. 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 United States National Museum; Smithsonian Institution; United States. Dept. of the Interior. Washington : Smithsonian Institution Press, [etc. ]; for sale by the Supt. of Docs. , U. S. Govt Print. Off.
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