184 MORRILL. [Vol. XI. 



tion of gold chloride for one hour, then rinsed in distilled water 

 and placed in a 10% solution of formic acid, and kept in the 

 dark for twenty-four hours. Very little difference was found 

 in the results obtained by treating the tissue first with 10% 

 formic acid for fifteen minutes and then for fifteen minutes 

 with I % gold chloride. The gold was reduced in this case in 

 a weak solution (2 or 3%) of formic acid in the direct sunlight. 



Tissues stained by these methods were imbedded in parafifine 

 by the usual methods, and sections 2 mm. in thickness were cut 

 and mounted in Canada balsam. 



The rapid Golgi method gave much more complete demon- 

 strations of the distribution of the nerves in the epidermis than 

 any other method. 



Histology. 



Cross sections of the free rays of both species of PrionoUis 

 were made about half an inch from the tip of the ray. In P. 

 palmipes the section is somewhat quadrilateral in form, but 

 three of the faces have reentrant angles, making seven imper- 

 fectly marked sides as shown in the outline (Fig. 5). 



Covering the epidermis of the free rays is a semi-transparent 

 layer composed of hyaline prisms, each forming a cap over a 

 single cell and probably secreted by it. A similar layer is 

 called the cuticle by Jourdan (4) in his paper on Peristedion. 

 The cuticle is easily separated from the underlying epidermal 

 cells by the action of reagents. It is thinnest over the papillae, 

 and thickest on the surfaces which look backward {Fig. 5 c) 

 when the ray is in the resting position. This cuticular layer is 

 very slightly stained by reagents, and shows no nuclei. 



The epidermis consists of five or six irregular layers of 

 closely crowded cells. The epidermis will be considered more 

 fully in connection with the nerve endings. 



Numerous nerve trunks of various sizes are arranged, as seen 

 in the section (Fig. 5 ;/), nearly parallel to the outer and inner 

 faces of the ray, but lie considerably below the skin. They are 

 closely crowded together around the flattened skeletal bones 

 (Fig. 5, I and 2) which occupy the center of the ray. The 

 sections of the parts of the axial skeleton are somewhat crescent- 



