298 Journal of Comparative Neurology afid Psychology. 



LIST OF ABBREVIATIONS 



c.t.c. — connective tissue cells. 

 e. — epidermis. 

 m.c. — marginal cells 



n. — nerve. 

 n.f. — nerve fiber. 

 n.f. ' — neuro-fibrillae. 



p. — pigment. 

 p.p. — primitive pore. 

 sen.c. — sensory cells. 

 sup.c. — supporting cells. 



Fig. I. The ventral surface of the bill of the Polyodon spathula, photograph, A. H. Cole. X-5-. 



Fig. 2. Two primitive pores (p.p.) seen in transverse section. The figure shows their relative 

 width and depth, the deep staining capacity of the epithelium of their bases, a nerve (")in cross-section, 

 and strands of neuro-fibrillae {n.f.' ) entering the base of a pore. This section was made from a specimen 

 taken from the dorsal surface of the bill and stained with gold chloride as above described. X^?- 



Fig. 3. A primitive pore in transverse section, showing the character and thickness of the epithe- 

 lium (e) upon the surface of the bill, the marginal cells (m.c.) of the sides of the pore, the supporting 

 cells (sup. c. ) and sensory cells {sen.c. ) of the base of the pore, and pigment (p.) in the connective tissue 

 about the pore. X 1 50. 



Fig. 4. A large group of primitive pores, viewed from its deep surface. It shows the variation 

 in size of the pores, the arrangement of them into smaller groups, the branching and distribu- 

 tion of the medullated nerve fibers to the group, and the accumulation of pigment among the pores. 



Fig. 5. The base of a primitive pore cut so as to show the deeper portions of the sensory and 

 supporting cells, and strands of neuro-fibrillae («./.') approaching and breaking up among them. X90' 



Fig. 6. Three sensory cells (sen.c.) and two supporting cells (sup.c), with the termination 

 of neuro-fibrillae (n.f.' ) upon them. 



