68 



SYDNEY EVANS JOHNSON 



Lat Cn 



Grp, 







V 



(© 



. :^ 



CI?;?. 



8 3 



Fig. 81 Longitudinal section of the lateral canal of a Squalus pup, showing 

 two lateral ramuli, fiber zone, and sensory epithelium. X 136. 



Fig. 83 Transverse section of lateral sensory column of the same specimen 

 (fig. 82). X 1160. 



observations on both Mustelus and Squalus show that the 

 nerve fibers grow from the gangUon cells. There is no evidence 

 of addition to the nerve from cells of the integument. The 

 latter are developed into secondary sense cells (Harrison '03). 



V. SUMMARY, CONCLUSIONS AND COMPARISON OF THE FORMS 



STUDIED 



The sensory canal system embraces two sets of organs desig- 

 nated canal organs and surface or pit organs respectively. As 

 the terms imply, the former are enclosed within epithelial canals 

 and the latter he at the surface of the skin or in shallow pits. 



■^ 



