2OO METCALF AND JOHNSON. 



ogy of this group of cells with certain portions of the eye of 

 Cyclosalpa pinnata and Cyclosalpa chamissonis will later be dis- 

 cussed. 



Small groups of apparent rod-cells are found in the peripheral 

 cellular layer of the ganglion, (Fig. 5, cy, cy' , cy"). They may 

 perhaps be called small eyes, because they are made up of cells 

 with thick-walled basal ends, similar to the rod-cells of the large 

 eye. An enlarged drawing of one of these groups is shown in 

 Fig. 1 1. The cells of these small eyes are not elongated as are 

 the rod-cells of the large eye, and their nuclei are the same size 

 as those of the ordinary ganglionic cells. More or less similar 

 smaller eyes occur in the ganglia of the chain forms of Cyclosalpa 

 pinnata, C. chamissonis, Salpa cylindrica, S. runcinata-fusiformis, 

 lasts hexagona, I. costa-tilcsii, Pcgca scntigcra-confcdcrata and 

 Thalia democratica-micronata. Compare Fig. 18, Plate IX., which 

 shows their position and appearance in Cyclosalpa pinnata. 



There is no pigment present in these small eyes of any species 

 described except Salpa costata-tilcsii. Goppert assumes that these 

 eyes are functional optic organs, but the absence of pigment 

 makes the correctness of this assumption doubtful. 



The small groups of rod cells which occur in the ganglion of 

 Cyclosalpa dolichosoma-virgula vary in number and position, but 

 all have about the same structure. Their cells are about the 

 same size as the ordinary peripheral cells of the ganglion and 

 seem to be developed from these merely by the formation of the 

 peculiar outer glassy layer indicated in the figures (Plate VIII., 

 Figs. 5 and ii)by the heavy black lines. The glassy outer por- 

 tion of one of these cells resembles in histological character the 

 glassy outer layer, which we have called the thickened cell-wall, 

 seen at one end of any rod-cell of the larger eye, but the cells 

 are of quite different shape, being spheroidal, or irregularly poly- 

 hedral, instead of cylindrical. There seems to be a general ten- 

 dency in the chain forms of the different species of Salipidce to 

 form from the smaller cells of the ganglion such groups of im- 

 perfect rod-cells. 



Each of the two later o- ventral outgrowths which push out 

 from the ganglion toward the glands consists of cells of two sizes. 



