No. I.] PECTORAL APPENDAGES OF PRIONOTUS. 1 85 



shaped with their long diameters extending in an antero-posterior 

 direction. The parts of the axial skeleton are separated inter- 

 nally by connective tissue, which holds them firmly in place. 



The blood vessels (Fig 5, b) are arranged in four groups 

 about the central skeleton, each face having its group. 



In P. cvolans the section is much more nearly quadrilateral 

 in outline (Fig. 6). The same general arrangement of parts 

 exists as in P. palmipcs, as will be seen from the figures. 



Over the papillae (Fig. 7) of the free rays the cells forming 

 the outer layer (Fig. 7, /) of the epidermis in P. palmipes are 

 somewhat columnar in shape. The outer portion of each cell 

 stains very imperfectly, while the large nucleus which is found 

 near the inner end takes the stain readily. 



The inner row of cells (Fig. 7, b) has at this portion of the 

 ray been transformed into a layer of cylindrical epithelial cells 

 placed perpendicular to the basement membrane on which it 

 rests. This layer constitutes more than one-third of the entire 

 thickness of the epidermis. 



There seems to be considerable uniformity in the position 

 of the nuclei of the outer layer of cells, since all are placed 

 with their long axes transverse to the long axis of their respec- 

 tive cells. In the inner row of cells (Fig. 7, b) the long axes 

 of the nuclei and cells coincide. The intermediate rows of epi- 

 dermal cells have not undergone any modification except that 

 large spindle-shaped, deeply staining cells arranged perpendicu- 

 larly to the surface of the papillae and broadest on their inner 

 ends are found quite regularly among them, but varying in 

 position. 



The epidermis is still more highly modified on the surfaces 

 forming the reentrant angle. The outer layer has become 

 thickened, and the cells have assumed a spindle form. The 

 inner layer is similar to that found over the papillae, but much 

 thinner, and the intermediate cells have become more than twice 

 as numerous as they are elsewhere on the ray. The spindle- 

 shaped cells are more abundant than over the papillae. There 

 is no sharp line of demarcation between the epidermis on this 

 portion of the ray and that over the papillae, as one passes 

 gradually into the other. 



