No. 4-] 



AMPULLAE OF THE SELACHII. 



169 



contiguous the cytoplasm appears like a single thin line (Fig. 

 4, ,?.). Outside this layer of cells is a sheath of connective 

 tissue of varying thickness constituting the larger portion of 

 the wall of the tube (Fig. 4, con. /is.). 



The histology of the ampulla is best studied in a longitudinal 

 section. Two regions, distinguished by the character of the 

 lining cells, are to be recognized. First, the centrum cap is 

 covered on its upper surface with a single layer of cells usually 



FIG. 3. Cross section of ampulla below plane of centrum cap: a.c., ampulla centrum; a.pkt., 

 ampulla pocket ; a.prt., ampulla partition ; con.tis., connective tissue. x 63. 



FIG. 4. Longitudinal section of upper portion of ampullary pocket and of tube: con.tis,, connective 

 tissue; d.c., deeper layer of cells; p.c., peripheral layer of cells ; i.e., tube cells ; z., point where 

 two cells of tube wall meet, x 465. 



almost cubical in shape (Fig. 5, c.c. 1 }. The oval nuclei are 

 large. In many sections the cytoplasm toward the lumen of 

 the tube pushes out into a blunt process, the line of cells in 

 the section then having the appearance of irregularly placed 

 saw-teeth. This same single layer of cells covers the under 

 side of the centrum cap (Fig. 5, c.c.i), where the latter arches 

 over the ampullary compartments. At the edge of the cap 

 the cells become more elongated, often spindle-shaped (Fig. 5, 

 c.c. 2 }. The partition walls near the centrum are likewise cov- 



