M. M. METCALF ON THE EYES AND SUBNEURAL GLAND OF SALPA. 335 



maxima, Salpa hexagona and Salpa costata-Tillesii, and that in this 

 species, as in those, there has occurred a shifting of the developing eye 

 of the chain form that has caused the originally ventral surface to 

 become dorsal, as was seen in the development of the chain Cyclosalpa 

 pinnata, and is shown by the innervation to have occurred in the develop- 

 ment of all the members of the group just mentioned. 



SALPA CORDIFORMIS-ZONARIA. 



This species shows quite aberrant features in the eye of both the 

 chain and solitary forms. The eye of the solitary form agrees in histo- 

 logical character with the eye of the solitary Cyclosalpa pinnata or Salpa 

 cylindrica ; i. e., it has the typical histological structure. (See Figs. 14 

 and 15, Plate LIV.) In shape, however, it shows a divergence from the 

 eyes of all other species. The anterior ends of the horseshoe-shaped eye 

 project dorsalward and obliquely to the right and left (Fig. 5, Plate LVI). 

 Only the posterior curved part of the eye rests on the surface of the 

 ganglion. Although the shape is different from that of the typical eye 

 of the solitary form, it is really but a slight modification of that eye, the 

 anterior limbs of the horseshoe having been elevated above the ganglion, 

 losing contact with it. It is important, however, as the only considerable 

 modification shown in the shape of the eye of the solitary form of any 

 species of salpa or cyclosalpa. 



In the chain form the eye has the typical position on the dorsal face 

 of the ganglion (Plate LVI, Fig. 3 ; Plate LIV, Figs. 11, 12 and 13). It is 

 oval in shape, with its long axis a little inclined to the long axis of the 

 body. A study of the histological structure and the arrangement of the 

 histological elements shows that here again we have represented, in a 

 disguised form, the anterior and posterior regions of the eye, comparable 

 to the similar regions found in the large eye of the chain Salpa run- 

 cinata-fusiformis and others. Fig. 13, Plate LIV, shows the condition 

 found. It represents a vertical section in the direction of the long axis 

 of the eye, a little on one side of this axis. The rod cells of the typically 

 basal portion are seen at s'. They are seen to connect directly with the 

 fibers of the optic nerve. The rod cells of the typically apical portion are 

 seen at s". The eye of this species is very compact ; the apical portion 

 being brought back under the basal portion, so that the thick-walled ends 

 of the rod cells of one region are in close connection with the thick- walled 

 ends of the rod cells of the other region. In Fig. 13 we see the pigment 



