216 FRANKLIN PARADISE JOHNSON 



the connective tissue gradually grows liigher and higher, and 

 in so doing, moulds the epithelium of the villi into that of the 

 glands. Schirman ('98) describes the disappearance of the villi 

 of the large intestine of the guinea-pig in an entirely different 

 manner as follows : 



Die embryonalen Zotten des Dickdarms bestehen beim JMeer- 

 schweinchen zu vier Fiinfteln ihrer Lange einzig aus Epithelzellen, nur 

 das basale Flinftel der Zotte enthalt einen axialen, Blutgefiisse fiihr- 

 enden Bindegewebstrang. Nur dieses basale Fiinftel bleibt erhalten 

 und geht in der Bildung der Lieberkiihn'schen Driisen auf, der grossere 

 Rest wird zuriickgebildet, er zerfallt. 



It is certain that no such process as Schirman has described 

 takes place in the human large intestine. 



The disappearance of villi is indeed difficult to explain in 

 mechanical terms. All that can be said with certainty is that 

 the villi gradually develop, reach a certain maximum height, 

 and then gradually fade out. It is of interest in this connection, 

 however, to note that the effect of distention of the large intes- 

 tine, caused by a storing up of meconium, brings about a dis- 

 appearance, or at least a partial disappearance, of the villi. It 

 is hardly probable that mechanical distention of this kind is 

 connected with a lasting disappearance of villi of the large intes- 

 tine, for they do not disappear permanently from the small 

 intestine, where distentions are also found. 



Development of the plicae seynilunares coli 



The before described longitudinal and oblique folds of the 

 epithelium of the colon are in no way related to the later plicae 

 semilunares. They disappear with the development of villi, and 

 therefore, are only transient structures. The larger plicae semi- 

 lunares are of later origin, and as they run an oblique course 

 along the wall of the intestine, they have been studied from both 

 cross and longitudinal sections. The observations shown in 

 table 1, have been made to indicate the condition of the inner 

 surface of the large intestine as regards these folds. 



