William A. Hilton 479 



These glands of Lieberkiihn were first described by Malpighi in 

 1688 and later by Lieberkiihn in 1745. 



The occurrence of these structures in fishes is doubtful, in Amphibia 

 and Reptiles there are small areas where new epithelium is formed, 

 or in other words, centres of cell generation; these little areas may be 

 homologized with the crypts of higher forms. In birds there are crypts 

 which are similar to those of mammals in all respects except size. 



As to the manner of their development there have been many dif- 

 ferent interpretations by the investigators who have given them atten- 

 tion. Voigt, 99, summarizes the work which has been done on the 

 development of these crypts, so a short review is all that is necessary to 

 repeat before beginning the description of the crypts in the white rat. 



Kolliker, 61, describes Lieberkiihnen crypts in the beginning as deep 

 out-growths of the epithelium, that is, down-growths. 



Earth, 68, thought that the glands did not arise as down-growths 

 (Ausstiilpungen) of the epithelium, but. that under the epithelium was 

 a mesodermal layer from which villi and glands were developed. In 

 the large intestine a similar development was said to take place. 



Brand, 77, arrives at the following results: In the large intestine 

 between the papillae which develop from the surface, the glands are 

 slowly formed. In the small intestine the villi are thickened at the 

 bases, these touch and unite with each other and so separate walls 

 appear, so the tube-like hollow Lieberkiihnen glands are formed. 



Kolliker comes to express similar views in his text-books of 79 and 

 94, and later editions of his works give the development much as the 

 following. 



0. Schultze, 97. In the stomach and large intestine, papillse or villi 

 are described which unite by means of low folds, so that little dimples 

 appear, from each of these a deep insinking or end of a gland appears. 

 Later these connecting folds or borders reach to one-half the height 

 of the villi; so now the surface of the intestine appears as a honey- 

 comb. At last the binding folds reach the top of the villi and at 

 their disappearance the whole mucous membrane has the appearance of 

 a honeycomb, in the mucosa are numerous glands which completely fill 

 up the space. 



In the small intestine there is a similar formation except that in the 

 depths between the villi, the surface of the mucosa furnishes net- 

 formed, binding folds and the epithelium from the so arising depres- 

 sions push in short hollow sprouts. The gland formation is not so 

 striking here because the villi during the formation of glands do not 

 dwindle, but on the contrary, become longer. 



