488 



HISTOLOGY 



by a columnar epithelium which lines the wide lumen without any am- 

 plification whatever, as was the case in other oviducts. The cells are 



columnar and have both a 

 thickened border and a line 

 of cilia. The secretion ap- 

 pears as a globule in the 

 cell body, and is discharged 

 as mucin is. 



A short distance below, 

 the tube narrows somewhat, 

 and its walls become thicker. 

 This region is not extensive, 

 and forms a short but promi- 

 nent enlargement called the 

 shell gland. An examina- 

 tion of the epithelium of 

 this organ shows that it is 

 lined by much the same kind 

 of epithelium, except that 

 the cells are much larger and 

 the surface is thrown into 

 shallow tubular glands 

 whose cells have undergone 

 no marked differentiation, 

 and which are probably ob- 

 literated by stretching when 

 the large egg passes through. 

 In the lowest part of the 

 oviduct, the walls are much 

 thicker, the lumen larger, 

 and the epithelial lining is 

 changed from the columnar 

 form of the preceding parts 

 to a very peculiar, distally 

 elongate, stratified form (Fig. 

 458). A cell of the basal layer 

 of this epithelium extends 

 as a ribbon-like fiber for almost halfway out to the lumen. The outer 

 cells are wedged in between the ends of basal cells and form a somewhat 

 irregular distal boundary to the epithelium. Here they show signs of 

 degeneration. The possibility remains that some of the cells extend 

 from basement membrane through to distal surface, and that the layer 

 is theoretically a simple epithelium. Even were this so, the practical 



cp 



FIG. 457. Parts of the opposed epithelia in the ova- 

 rian tube of the fish, Pterophryne histrio; d.s., distal 

 surfaces of the two epithelia; nid.ep., nidamental 

 epithelium; rep.ep., reproductive epithelium in out- 

 line; ov., outlines of two ova lying in follicles inside 

 the reproductive epithelium. X 840. 



