1 68 



PEABODY. 



[VOL. I. 



toward the center. The lumen at the base of the ampulla is 

 thus divided into the above-mentioned eight to twelve com- 

 partments (Fig. 3, a.pkf). A 

 columnar structure (Fig. 2, a.c.} 

 to which the partitions run, is 

 formed in the center of the am- 

 pulla. To this structure Boll has 

 applied the name "centrum." 

 The centrum increases in diam- 

 eter considerably above, so as to 

 form a slightly concave, plate- 

 ccn.us. iik e ca p (Fig. 2, a.c.c.}, which 

 covers over a portion of the com- 



Fi<;. 2. Longitudinal section of ampulla partmClltS beneath. Ill longitU- 

 through centrum, plane of section passing 



through an ampullary pocket on the left dinal SCCtlonS of the ampulla 



side of the figure and through a partition . . . 



wall on the right : a c., ampulla centrum ; taken thrOUgh a partition (tig. 



a c.c., ampulla centrum cap : ,,.., ampulla , . . , , r1rrf> nf 



nerve; a.frt., ampulla partition; con t-s., 2 )> - Q g e 



connective tissue; ., ampulla tube. < 5.- the part i t i on C UrVCS Upward aS 



it passes from the centrum to unite with the outer wall. 



The average diameters of the ampullae of a dogfish 1.02 m. 

 long are as follows : 



In the supra-orbital-buccal groups 



In the hyoid groups 



In the mandibular groups 



T 9 o mm. 



T V mm. 



mm. 



Histology of Tube and Ampulla. In histological structure the 

 tubes are comparatively simple. They are lined with a single 

 thin layer of epithelial cells. In surface view the outlines of 

 the cells, most clearly made out from a silver nitrate impreg- 

 nation, are seen to be polygonal. The oval nuclei have a 

 diameter about one-third that of the cells. In cross sections 

 (Fig. 4, i.e.} the nuclei appear as thin ellipsoid bodies, staining 

 deeply. Nucleoli are visible. The shape of the cell body is 

 more difficult to determine, since the nucleus occupies so large 

 a part of its thickness. But after using several methods of 

 fixing and staining I am confident the section of the cell is 

 spindle-shaped, the thickness decreasing from the center 

 toward the periphery, until at the point where two cells are 



