LATERAL SENSE ORGANS OF SQUALUS SUCKLII 281 
clusters of these cells between adjacent surface tubules, and the 
tubules, in turn, are more numerous than the segments of the 
vertebral column. Nor is there any marked regularity in the 
number and size of the individual clusters of sensory cells. 
While the sensory column is thus essentially continuous through- 
out the entire length of the sensory canal it shows considerable 
Fig. 1 Transverse section of the entire sensory canal of a Squalus sucklii 
garter. Camera lucida sketch. Iron haem. tech. X 432, 2 off. Can., canal 
wall; Fb.Zn., longitudinal fiber zone; Sn.Cl., secondary sensory cell; Sn.Col., sen- 
sory column; Spn., spindle cells. 
variation in thickness. It becomes gradually thinner posteriorly 
and, as in Mustelus, it is usually thinner between adjacent 
ramuli of the lateral nerve. The base of the column of sensory 
cells is limited by a continuous basilar membrane. 
The same types of cells can be distinguished in the lateral 
sensory epithelium of Squalus sucklii as were found in the sensory 
