282 SYDNEY E. JOHNSON 
column of Mustelus and of Squalus acanthias. The hair cells or 
secondary sense cells are large, pear-shaped, and have centrally 
placed nuclei. In many specimens hair-like processes could be 
seen at their distal ends, but whether one or more for each cell 
has not been determined. The relative length of the cells is 
usually one-half to two-thirds the thickness of the sensory 
Fig.2 Longitudinal section 0 the lateral sensory column (Sn. Col.) of Squalus 
suckhi (adult). The sensory epithelium was drawn with the aid of a camera 
lucida {rom an iron haematoxylin preparation, and the nerve fibers were put in 
free hand from pyridine silver sections. The outlines of the canal wall (Can.) 
and the surface tubule (7'ub.) are not drawn to scale but are greatly reduced in 
order to conserve space. For correct proportions, see figure 1. Sensory column, 
x 650, 4 off. Fbr., terminal fibrillae; Fb.Zn., longitudinal fiber zone; Grp., 
one group of secondary sensory cells (hair cells). 
column. Spindle-shaped cells, basilar cells, and columnar cells 
constitute the supporting elements (see figs. 1, 2, 3 and 10). 
The rest of the canal wall is formed by a double layer of epi- 
thelial cells, both layers of which are continuous with the walls 
of the surface tubules and also with the columnar and stratified 
layers of the epidermis. 
