OBSERVATIONS ON STRUCTURE OF CELLS AND NUCLEI. 131 



free surface of the epithelial cells covering the villi, are independent 

 of the above bright cuticle or border substance. I have, namely, 

 seen in sections of villi of small intestine, and also in sections of 

 large intestine of pig — the intestine had been hardened in the 

 mixture of chromic acid and spirit — groups of epithelial cells in 

 which the projecting fibrils could be very beautifully seen lo'itJi- 

 out anjj hricjlit border substance beincj inesent. There were other 

 groups of epithelial cells in which the other arrangement pre- 

 vailed, viz. the striae seen more or less dimly apparently in the 

 bright border substance. Arguing from this fact, one might 

 say that if those projecting fibrils can be present without that 

 bright border substance, they cannot be contained in it, for if so 

 the absence of one must necessitate the absence also of the other. 



But before definitely accepting this, we have to see whether 

 this same appearance can be observed also in the intestine of other 

 animals, especially carnivorous animals, where this bright border- 

 substance is present to a very considerable extent. And I have 

 indeed noticed on villi of small intestine of dog and cat that in 

 some parts the epithelial cells show beautiful fibrils projecting 

 beyond the free border without there being present any bright 

 border substance. 



(^) Of Lieberkulm's crypts. — The epithelial cells lining the 

 crypts of Lieberkiihn are identical with those of the surface of 

 the mucous membrane, both as regards the structure of the cell 

 substance and that of the nucleus (see fig. 2, PI. VII). AUI 

 said above about the arrangement of the intracellular and intra- 

 nuclear network applies also to the epithelium, and it is therefore 

 unnecessary again to repeat it.^ True, there are certain differ- 

 ences, but these refer merely to the shape and size of the cell 

 and its nucleus. Thus, comparing the epithelium lining Lie- 

 berkiihn^s crypts of the small intestine with that covering 

 tlie villi — of course in the same animal — it will be found 

 that the epithelial cells of the latter are conspicuously longer, 

 i.e. more columnar than those of the former, and that the 

 nucleus of the epithelial cells of the viUi is more regularly 

 elliptical than that of the epithelial cells lining the crypts of 

 Lieberkuhn in the same parts, the nucleus in many cells of the 

 latter being circular. Again, comparing the epithelium lining 



^ P. E. Schulze, in liis work on epithelial and goblet cells, to be referred 

 to several times in the following pages, maintains that the epithelial cells 

 of the crypts of Lieberkiihn diifer from those covering the villi, inasmuch 

 as the free border of the former is open, whereas that of the latter is closed 

 by the thick bright border substance mentioned above. This distinction 

 cannot be, however, admitted, because there is in both instances the same 

 bright border substance and the same striation of it, and consequently the 

 explanation of the nature of these appearances must be the same in both 

 kinds of epithelial cells. 



