. Bulletin - United States National Museum. Science. vol. 2,pt. 2.] A TAXONOMIC STUDY OF THE SALPIDAE METCALF. 105 its anterior ends elevated above the surface of the ganglion and not in contact with it. The ends are spread apart also, so that the typ- ical horse-shoe shape is distorted to crescent shape. At the lower edge of the ganglion, on each side, there is a wide rather thin outgrowth (ey) of very large irregular cells whose walls are in places thickened, resembling exactly the degenerate rod-cells of the other species of Salpidae. These outgrowths must be inter- preted as accessory eyes
. Bulletin - United States National Museum. Science. vol. 2,pt. 2.] A TAXONOMIC STUDY OF THE SALPIDAE METCALF. 105 its anterior ends elevated above the surface of the ganglion and not in contact with it. The ends are spread apart also, so that the typ- ical horse-shoe shape is distorted to crescent shape. At the lower edge of the ganglion, on each side, there is a wide rather thin outgrowth (ey) of very large irregular cells whose walls are in places thickened, resembling exactly the degenerate rod-cells of the other species of Salpidae. These outgrowths must be inter- preted as accessory eyes. In only two other species of Salpidae (Salpa fusiformis and Ritteria Tiexagona) does the solitary form have accessory eyes, and these are mere ventral extensions of the mass of rod-cells in the anterior ends (S. fusiformis, fig. 76, p. 91), or on the side (R. Tiexagona, figs. 39 and 40, p. 66) of the horseshoe-shaped eye. The structures most similar to these optic lateral outgrowths in the solitary Iasis zonaria are the ovoid and somewhat smaller masses of degenerate rod-cells, seen as outgrowths from the sides of. Fig. 96.—Iasis zonaria, solitary form, cross section through the ganglion, the anterior limb of the dorsal eye, and the lateral outgrowths from the ganglion, x 200 diameters. From Metcalf (1893, c). the ganglion in the aggregated Ritteria Tiexagona (fig. 45, p. 70 and fig. 47, p. 71). The usually conservative solitary form has, in Iasis, de- parted widely from the general type in the character of the accessory eyes as well as in the form of the dorsal eye, and in the character of the musculature, including the reduction in the number of the body muscles and the peculiar character of the oral and atrial muscles. IASIS ZONARIA, aggregated form. This zooid (figs. 97 and 98) is about as asymmetrical as is the aggregated Saljm cylindrica (fig. 84, p. 96), the asymmetry being shown in the lateral positions of the posterior protuberance and atrial siphon. There are five
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