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 broad body muscles, all but the first continuous 

 across the mid-dorsal line and all widely interrupted ventrally. 

 Body muscle 5 on the right side is divided into an anterior and a 



