136 



BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



Fig. 126.— Pegea confedeeata, aggregated form, 

 somewhat oblique vertical section of the gan- 

 glion and dorsal eyes. x 170 diameters. from 

 Metcalf (1893, c). 



of the eye (posterior limbs) has its pigment ventral and its rod-cells 

 dorsal and the optic nerve passes up over the limbs of the eye to reach 

 its dorsally lying rod-cells. In Pegea these relations are exactly 



reversed in the corresponding 

 portions of the eye {e'). The 

 pigment is dorsal and the nerve 

 fibers reach the rod-cells di- 

 rectly from the ganglion. 



Of course, if no inversion 

 has occurred in the eye of this 

 species, that portion of the eye 

 ie"), which in Cyclosalpa lies 

 anterior to the basal portion, 

 must in Pegea lie behind the 

 basal division. These are the 

 relations observed in Pegea. 

 Posterior to that portion of 

 the eye which we have labelled 

 e' lies a second division {e") whose rod-cells are dorsal and whose 

 pigment is ventral. The optic nerve passes between the two por- 

 tions of the eye to reach the rod-cells of the second portion {e"). This 

 lack of inversion of the dorsal eye in the aggregated zooid of Pegea 

 marks this subgenus off sharply 

 from all the other subgenera ex- 

 cept probably Traustedtia, which 

 we will soon discuss. 



In the ganglion of Pegea con- 

 federata are two accessory eyes 

 (fig. 127), which I have before 

 described as follows (Metcalf. 

 1893, c): 



Two masses of similar, thick-walled 

 cells are present in the ganglion, one on 

 the right, the other on the left, a little 

 above the midpoint, of the lateral faces 

 of the ganglion. These cells exactly re- 

 semble 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, 

 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 periphery of the ganglion. In the 

 former, the nuclei contain many small chromatin granules, and no very large nucleolus • 

 The other cells of the ganglion are of two sorts, the one sort small, with small nuclei. 

 These are utterly different from the cells we are discussing. The other kind of ganglion 

 cells is larger, about equal in size to the rod-cells of the eye. They have the same sized 

 nuclei, but in these the chromatin is nearly all collected into a large nucleolus, giving 

 a decidedly different appearance from the nuclei of the rod-cells. Besides this their 



Fig. 127.— Pegea confederata, aggregated 

 form, cross section of dorsal eyes and of 

 ganglion, showing also tne pair of accessory 

 eyes in the ganglion. x 170 diameters. from 

 Metcalf (1893, c). 



The arrangement of chromatin in their 



