456 ALDEN B. DAWSON 



c. Epithelnwi of cloaca 



The epithelium Hning the cloaca of the male Xecturus is not 

 simple in any region. In the cephalic portion it is two-layered, 

 consisting of a superficial columnar or cuboidal layer and a deep 

 somewhat flattened replacing layer. In certain areas the outer 

 layer of cells is ciliated ; in others, the outer cells are of the tall 

 mucous type, and in still others, they are unmodified. More 

 caudad the number of cell layers is gradually increased until at 

 the margins of the cloacal aperture a stratified epithelium simi- 

 lar to that of the external surface of the body is found. Xo 

 Leydig cells, however, are present within the cloaca, although 

 they occur in considerable numbers in the epidermis a short 

 distance from the cloacal orifice. 



Dorsally, in the region of the paired urogenital papillae, a 

 small ciliated area is found. More cephalad, toward the rec- 

 tum, the epithelium is non-ciliated and of the mucous type. 

 Caudad, on the portions of the dorsal wall through which the 

 pelvic tubules open, i.e., on the Y-shaped area, the median dor- 

 sal groove and the dorsal walls of the lateral furrows, the super- 

 ficial cells, for the most part, are unmodified, resembling in their 

 staining reactions the cells which in other areas possess cilia. 

 Locally, however, groups of tall clear cells, typically mucous 

 in appearance, are found. It seems possible, therefore, that the 

 unmodified cells may be young or rejuvenating mucous cells. 



Ventrally, in the region of the orifice of the urinary bladder, 

 the cloacal wall is covered by a mucous epithelium, but more 

 caudad ciliated cells are found, chiefly along the summits of the 

 longitudinal folds. Also scattered patches of ciliated epithelium 

 link up the ventral ciliated portions with the dorsal ciliated area. 

 The high, thin ridges of the ventral trough are for the most part 

 covered with a two-layered ciliated epithelium, but the conical 

 elevations, on which the cloacal tubules terminate, have a mu- 

 cous epithelium. The transition from one tj^pe of epithelium to 

 the other is abrupt. 



The slender internal papillae, through which the cloacal tu- 

 bules open, with the exceptions of small areas at their bases, do 



