KiSTLER, Primitive Pores of Polyodon. 297 



these peculiarities, the arrangement of the cells and the distri- 

 bution upon them of nerves, soon to be described, the writer has 

 concluded that these last described cells are sensory, and those 

 first described are supporting. 



According to van Wijhe (2) and Collinge (i) the nerves sup- 

 plying the sensory canal system of Polyodon are the trigeminus, 

 the facialis and the vagus. The findings of these men differ as 

 to some of the smaller branches of the nerves. The writer has 

 found them in general to be as described by Collinge, but be- 

 cause of the complexity and communication of the nerve groups 

 more work must be done upon them to determine the exact dis- 

 tribution of each. 



In the regions where primitive pores are found, there are many 

 medullated nerve trunks which in the immediate vicinity of a group 

 of pores send off branches to it (Fig. 4). These branches contain 

 only a few fibers which separate from each other, divide once or 

 twice, then lose their myelin sheaths and immediately enter the 

 bases of the primitive pores (Fig. 4). The axis cylinder after 

 losing its myelin sheath appears as a dense strand of neuro-fibril- 

 lae which divide and subdivide many times forming an end-brush 

 (Fig. 5). As the branches of this end-brush enter the epithelium 

 at the base of a pore they spread out and end in minute filaments 

 upon both the sensory and supporting cells, as represented in Fig. 6. 



In closing, the writer must emphasize the fact that the struc- 

 ture of the primitive pore is entirely unlike that figured and de- 

 scribed by Collinge (i). Whatever the function of these numer- 

 ous organs may be, it is certain that from a structural standpoint 

 they possess the characters of a sense organ. 



BIBLIOGRAPHY. 



1. Collinge, Walter E. The Sensory Canal System of Fishes. Quarterly Journal of Micro- 



scopical Science, London, vol. .36, pp. 499-537. 1894. 



2. Wijhe, J. W. van. Ueber das Visceralskelett und die Nerven des Kopfes der Ganoiden und 



von Ceratodus. Neiderland. Arch. /. Zool., Bd. 5, pp. 207-320, Taf. XV, XVI. 1882. 



3. Allis, E. p. On Certain Features of the Lateral Canals and Cranial Bones of Polyodno 



folium. Zool. Jahrh; Abt. Anat. u. Ont. d. Tiere, B. 17, H. 4. 1903. 



