. Bulletin - United States National Museum. Science. vol-. 2, ft. 2.] A TAXONOMIC STUDY OF THE SALPIDAE METCALF. 117 Fig. 110.—Thalia democratica, aggre gated form, dorsal view of gan GLION AND EYES. X 362 DIAMETERS From Metcalf (1893, c). probable homologies appear when we realize that the anterior rota- tion of the eye, observed in the development of Cyclosalpa pinnata (fig. 12, p. 25) occurs in the same way in Thalia democratica but has gone about one hundred and twenty degrees further, the ganglion itself sharing in this rotation, as is clearly shown by the development of the eye and
. Bulletin - United States National Museum. Science. vol-. 2, ft. 2.] A TAXONOMIC STUDY OF THE SALPIDAE METCALF. 117 Fig. 110.—Thalia democratica, aggre gated form, dorsal view of gan GLION AND EYES. X 362 DIAMETERS From Metcalf (1893, c). probable homologies appear when we realize that the anterior rota- tion of the eye, observed in the development of Cyclosalpa pinnata (fig. 12, p. 25) occurs in the same way in Thalia democratica but has gone about one hundred and twenty degrees further, the ganglion itself sharing in this rotation, as is clearly shown by the development of the eye and ganglion in the buds and by the arrangement in the adult of the ectodermal epithelium over the originally dorso-anterior face of the ganglion, which is now ventral. If, in imagination, we rotate the ganglion back one hundred and twenty degrees to a position comparable to that in, say, Salpa fusiformis (fig. 79, p. 92), we see that in position relative to the ganglion,and in the relative position of the rod and pig- ment cells, the anterior portion of the eye in Thalia democratica(ex) is compar- able to the large accessory eye (ex) in the ganglion of Salpa fusiformis. Its pigment layer, present in Thalia, is want- ing in Salpa. The two posterior por- tions of the Thalia eye (e'l and e'2) represent, then, the large dorsal eye of the true Salpae, or rather the proximal portion of this eye, as is shown by the position of rod-cells and pigment cells. The division of this eye into two parts, right and left, is a reversion to the condition seen in Cyclosalpa pinnata (figs. 7 and 8, pi. 2), in which the proximal portion of the large dorsal eye is divided into distinct right and left limbs. The inner- vation of the portions of the eye in Thalia agrees with this inter- pretation. The anterior portion (e") of the large dorsal eye, found in Cyclosalpa pinnata and in the other species thus far described in this paper, is lacking in Thalia, as is also the optic plug (e'"). < 3
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