192 FRANKLIN PARADISE JOHNSON 



The epithelium in the embryo under consideration (22.8 mm.) 

 varies in thickness in different regions. In the coUc ampulla 

 and vermiform process it is 0.056 mm. thick and shows three 

 to four rows of nuclei. In the remainder of the colon down to 

 the rectal ampulla, it is only 0.034 mm. in thickness and shows 

 but two to three rows of nuclei. At no place are the bounda- 

 ries between the cells distinct, but the free and basal surfaces 

 are well marked. 



In an embryo of 30 mm. the whole of the vermiform process 

 and the valve of the colon lie in the coelom of the umbihcal 

 cord. An examination of the interior of the colon in this region 

 shows the beginnings of two to three epithelial ridges. These 

 vary in height, the epithelium being 0.070 mm. thick, measured 

 through the summit of the largest ridge, while in the depressions 

 between them, it is only about 0.028 mm. thick. Three or four 

 rows of nuclei can be made out. The remainder of the colon 

 has an average diameter of 0.15 mm. Throughout its great 

 length the epithelial tube is still cylindrical in shape, having a 

 wall 0.048 mm. in thickness. Three or four rows of nuclei are 

 present. 



At 37 mm. the whole of the vermiform process still lies in 

 the umbilical cord. The epithelial ridges are higher than in 

 the former stages. In the base of the vermiform process there 

 are four of these, in the middle only three; in the beginning of 

 the colon, three or four. The highest ridge measures about 

 0.10 mm. in height and has three or four rows of nuclei. Between 

 the ridges the epithelium is only 0.042 mm. thick and shows 

 but two or three nuclear layers. The remainder of the large 

 intestine gradually decreases in size when followed caudally. 

 The portion which is to become the ascending colon is 0.27 mm. 

 in diameter; the transverse 0.22 mm.; and the descending colon 

 0.18 mm. The epithehum is about 0.056 mm. thick in all these 

 portions. A few vacuoles, such as have been found in the epi- 

 thelial walls of the stomach and oesophagus are present in the 

 colon of this embryo. 



In an embryo of 42 mm. the ridges of the epithelium are in 

 part replaced by true longitudinal folds. In the vermiform proc- 



