DEVELOPMENT OF DIGITIFORM GLAND 357 



smaller ones. In some adjacent places secondary ridges are still 

 fused at the periphery, while separated toward the center. There 

 thus appear to be, in transverse section, areas of connective tissue 

 completely surrounded by epithelium (fig. 17). These connec- 

 tive tissue masses are not entirely cut off but are continuous with 

 that surrounding the epithelium at some point anterior or pos- 

 terior to the section in question. 



In the 95 mm. stage the solid portion of the post-valvular 

 intestine (fig. 18) extends anteriorly about 0.9 mm. from the 

 entrance of the digitiform duct (fig. 26). The epithelium has 

 been so completely divided and subdivided into ridges that the 

 central part is less in diameter than the peripheral part of the 

 ridges themselves (fig. 18). The ridges are narrow as compared 

 with the preceding stage so that the surface of the epithelium 

 has increased in much greater proportion than the volume. 

 There are four principal ridges, each subdivided into two or 

 three parts (fig. 18). In transverse sections the ridges appear 

 as finger shaped processes. One of these ridges on the ventro- 

 lateral side is continuous with the duct of the digitiform gland 

 and from the external form it is impossible to tell the point 

 where the duct terminates (fig. 13). In a transverse section 

 however (fig. 14) it is seen that the duct enters by a side open- 

 ing into the dorsal side of the gut. 



Around the periphery each ridge has from four to six rows of 

 elongated nuclei, the long axes of which are at right angles to 

 that of the ridge. The center of each ridge is made up of cells 

 with irregularly rounded nuclei, although some are elongated, 

 parallel with the long axis of the ridge. Later, when the lumen 

 of the gut is re-established, the latter cells form the surface layer 

 of epithelium. Small isolated lumina are seen in the solid epi- 

 thelium toward either end of the solid region. 



In the 200 mm. stage the solid portion of the post-valvular 

 gut extends 2.2 mm. anterior to the ostium of the duct of the 

 digitiform gland. The gut has straightened (fig. 9). There are 

 four principal ridges upon the external surface, each subdivided 

 into two to four parts. They are of greater diameter at the 

 periphery than at the center of the gut. Histologically the 



