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FRANKLIN PARADISE JOHNSON 



the large intestine reaches its adult condition. The presence of 

 'transitory' villi has long been known, being first described by 

 Barth in 1868. Since then they have been studied by a number 

 of investigators, and several opinions have arisen in regard to 

 their manner of disappearance. However, most of the former 

 work has been done on lower animals, no one account giving a 

 complete history of the changes that take place in the human 

 embryo. 



In the present paper an attempt is made to describe in some 

 detail the mucosa of the large intestine and vermiform process 

 in a number of consecutive embryonic stages, and to present a 

 series of pictures made from wax reconstructions illustrating 

 the descriptions. The following account deals strictly with the 

 human embryo, and is based on a number of carefully selected 

 stages. The embryos used are arbitrarily di\dded into two 

 groups; — the younger stages, which were sectioned whole; and 

 the older stages, from which the various portions of the diges- 

 tive tube were removed from the embryo and sectioned sepa- 

 rately. The younger stages used were all obtained from the 

 Harvard Embryological Collection. They are as follows: 



The older stages were obtained from three different collec- 

 tions. I wish here to express my thanks to Prof. C. S. INIinot, 

 Harvard Medical School, Prof. C. M. Jackson, University of 

 Missouri, and Prof. Franz Keibel, Freiburg i/Br., for allowing 

 me the privilege of cutting out what portions of their embryos 

 I desired for my work. The list of older stages used is as follows: 



