UROGENITAL SYSTEM OF MYXINOIDS 



111 



The epithelium is composed of colmiinar cells, and is arranged 

 in a series of longitudinal folds or ridges. Wax models show that 

 these ridges branch and anastomose freely, but are always longi- 

 tudinal and the branching is dichotomous. The two branches 

 may run parallel to each other for a short distance and then 

 unite, or may unite with another ridge, or may end without 

 union to other ridges. A ridge may be only a fraction of a 

 millimeter long and be entirely unattached to any other ridges. 

 When free, the ends of the ridges rise gradually from the normal 

 height of the epithelium. 



The ridges are present in all parts of the duct, from the an- 

 terior to the posterior end, but at the former end, where the duct 

 is small, they may be only two or three in number (fig. 52) . As 

 the duct becomes larger, the ridges increase in number, and are 

 most numerous at the posterior end where the duct reaches its 

 maximum width. The ridges vary in number in a transverse 

 section in corresponding regions in different adult specimens, as 

 is indicated by the following table: 



There is considerable variation in the height of the ridges in 

 the same transverse section and in different parts of the same 

 duct. Figures 50 and 51 show the variation in the same sec- 

 tion. For a given duct the ridges are lower at the ends than in 

 the mid-region. 



The columnar epitheUal cells which form the walls of the duct 

 are shortest between the ridges. The nucleus is always located 

 about one-third the length of the cell from the basal membrane. 

 The cytoplasm is very granular throughout the entire cell body, 

 the granules being especially numerous and large at the distal 

 ends of the cells. Along the surface of the distal ends of the 

 cells are agglutinations of granules which project into the lumen 

 of the duct and resemble the mass of waste material which is 



