482 Intestinal Folds and Villi in Vertebrates 



to the crowding together of a number of nuclei. In later stages the 

 crypts are more easily recognized and they often take a deeper stain 

 than other parts of the epithelium, and because they extend deeper 

 into the submucosa than the simple spaces between villi. This last dis- 

 tinction of course only becomes evident as glands have passed their 

 earliest stage (Fig. 83). • 



The white rat is better adapted for a study of the disappearance of 

 villi from the large intestine than many other mammals because in 

 this form the villi persist some time after birth, twelve days or more, 

 and so may be studied in all stages. 



Villi begin their disappearance early. Just before birth the lower 

 large intestine is entirely free from villi and glands occupy nearly all 

 the surface of the rectum. 



In white rat, villi are formed first, then glands are developed in the 

 surfaces between villi and then later, villi disappear in the large intes- 

 tine. This order of development seems to be quite constant and at 

 first sight it appears as though the disappearance of the villi is in some 

 way associated with the development of glands. There is very little 

 literature upon this point. Minot, 92, states the general view as 

 follows : '' Villi also appear throughout the large intestine, but are 

 obliterated there by an upward growth of glands." 



As will be remembered Brand and Patzelt believed in the develop- 

 ment of glands by means of an upward growth not a downgrowth, and 

 the idea of Schultze and Minot that glands are in part formed by villi, 

 places their opinion midway between the upgrowth and downgrowth 

 theories of gland development; but so far as the disappearance of villi 

 is concerned the upgrowth theories and the views of Schultze and Minot 

 may be said to agree quite closely. Scherman in 98, studied the degen- 

 eration of the villi in the large intestine of guinea-pig and found that 

 the upper four-fifths of the villi were composed entirely of epithelial 

 cells; only the basal fifth was found to contain a core of connective 

 tissue. When the villi btgin to disappear by disruption, only this 

 basal part persists and passes into the formation of Lieberkiihnen 

 glands. He states that in other mammals there is no real degenera- 

 tion or disruption although the villi are used in forming the glands. 



Voigt, 99, did not determine how villi disappeared from the large 

 intestine, but found no disruption and no evidence to indicate that 

 villi had anything to do with the formation of crypts. He considered 

 the possible disappearance of villi by means of growth of the intestine, 

 but did not bring forward any proof of this possibility. 



