194 FRANKLIN PARADISE JOHNSON 



of myoblasts, the circular layer of the muscularis. This is in 

 turn bounded by a layer of mesenchyma and surrounding the 

 whole, except at its mesenteric attachment, a distinct serous 

 epithelium is seen. 



In passing ab-orally from the ascending colon into the trans- 

 verse colon, one of the four longitudinal folds just described 

 drops out, while a second becomes so much reduced in size that 

 it is scarcely recognizable as a fold (figs. 1 and 13). The two 

 remaining folds are distinct and about 0.06 mm. in height. The 

 epithelial tube has a diameter of about 0.27 mm. The remain- 

 ing features of this portion of the large intestine are similar to 

 those of the ascending colon. 



First appearance of goblet cells 



In the iliac colon (50 mm. embryo), the epithelial tube as a 

 whole is flattened from side to side. Its greater diameter is 

 0.36 mm., its lesser 0.18 mm. A considerable change in the 

 condition of folds is evident. They are shallow, irregular, and 

 more numerous than in the ascending and transverse colons. 

 A model of a small portion of this region is shown in figure 14. 

 The distinction between epithehal ridges and folds is here appar- 

 ent — only those protuberances, which have indented basal sur- 

 faces into which the mesenchyma extends, being considered as 

 true folds. Measured through the ridges the epithelium is in 

 places 0.084 mm. thick, while in the clefts between them, it is 

 only 0.028 mm. thick. The two types of cells described by 

 Lewis in the 42 mm. stage are distinct. A few cells on the 

 ridges have a protoplasm which is clearer than others, and are 

 shaped somewhat like goblet cells. Because these cells in the 

 next few stages take on more and more the appearance of goblet 

 cells until their identity cannot be doubted, I believe them to 

 be goblet cells in a very early stage of differentiation. Voigt 

 ('99) was able to distinguish goblet cells first in the rectum of a 

 human embryo of 70 mm. 



The ascending colon of an embryo of 55 mm. has a diameter 

 of 0.45 mm. Ten to twelve longitudinal ridges are found, but 



