330 JOHNS HOPKINS UNIVERSITY MORPHOLOGICAL MONOGRAPHS. 



eyes in the chain form of Cyclosalpa pinnata, indicates that it is homo- 

 logous with these eyes in the latter species. The presence of pigment 

 in connection with this structure in Salpa costata-Tillesii is a variation 

 which confirms the view that it is a light-perceiving organ, though the 

 typical histological character of the rod cells is not found. 



We come now to quite a distinct group of salpas, including Salpa 

 scutigera-confederata and another species, or more probably variety, not 

 recognized by Traustedt, which is probably the Salpa bicaudata of Salen- 

 sky and various authors. 



SALPA SCUTIGERA-CONFEDERATA. 



I have not been able to section the eye of the solitary form of this 

 species, for the Fish Commission collections included but one specimen. 

 In surface view (Plate LVI, Fig. 7) the eye almost exactly resembles that 

 of the solitary Cyclosalpa pinnata, i. e., it is typical. 



The dorsal eye in the chain form (compare Fig. 1, Plate LVI, which 

 represents the very similar eye of the chain Salpa bicaudata) shows two 

 well-marked regions, in one of which (the anterior) the pigment is dorsal 

 and the rod cells ventral, while in the other (the posterior) this arrange- 

 ment is reversed. The rod cells are of the same character as those of 

 the larger eye of the chain Salpa costata-Tillesii (compare Fig. 2, Plate 

 LV, with Fig. 10, Plate LIV). The pigment cells are so massed together 

 and so full of pigment that no structure can be made out. The optic 

 nerve arises from the dorsal part of the ganglion and enters the eye 

 between the pigment layer of the posterior region and the rod cells of 

 the anterior region. No intermediate cell layer can be distinguished. 

 The greater share of each region of the eye (all save the pigment layer) 

 is composed of thick-walled, polyhedral cells like those in Salpa costata- 

 Tillesii, chain form. The comparative thickness of the cell walls is 

 greater, however, in Salpa scutigera-confederata. 



Two masses of similar, thick-walled cells are present in the gan- 

 glion, one on the right, the other on the left, a little above the mid-point 

 of the lateral faces of the ganglion (Plate LV, Fig. 5, y). These cells 

 exactly resemble the peculiar rod cells of the large dorsal eye in size, 

 shape, character of nuclei, thickness of cell walls, in manner of staining, 

 and in their general appearance. The arrangement of the chromatin in 

 their nuclei and in the nuclei of the rod cells of the dorsal eye is very 

 different from that seen in the other cells of similar size found in the 



