COLUMNAR EPITHELIUM. 



Fig. XXIV. 



more generally held that the new epithelium-cells are produced by division of pre- 

 existing cells in the lowermost stratum. In the earliest condition of the embryo 

 there are special layers of cells, derived from the primitive embryonic cells, set aside 

 for the production of the epidermis and of the intestinal and glandular epithelium ; 

 and it is quite conceivable, and by some histologists considered most probable, that 

 the subsequent generations of epidermic and epithelial 

 cells by which the tissue is throughout life main- 

 tained, are derived by unbroken descent from the 

 original embryonic stratum. At the same time, the 

 reproduction of epidermis in cicatrices after wide 

 and deep destruction of the subjacent skin, implies 

 some other source of new cells ; unless indeed it be 

 supposed that the new cuticle grown exclusively from 

 the old at the circumference of the sore. Setting 

 aside this supposition, we might conceive the new 

 cells to come from the connective-tissue corpuscles of 

 the granulating surface of the new-growing skin ; and 

 a recent writer (Dr. Otto Weber) describes such mode 

 of reproduction of epidermis as actually observed by 

 him in the healing of wounds ; moreover, it may be 

 questioned whether, in certain situations, this may 

 not be the regular process by which the growth of 

 epithelium is maintained. 



When the lowermost cells are elongated and vertical, 

 it is difficult to conceive that they rise up as such, 

 and take their place in the upper strata ; for the cells 

 next above them are spheroidal in shape and smaller 

 in size. It seems more likely that they divide into 

 It might be supposed that an oblong vertical cell, 

 by division of its nucleus and separation of the upper portion of the cell-body, 

 produces a new and smaller cell, which rises up, while the parent cell maintains 

 its place, and lengthens out again for a repetition of the process. Dr. Schneider* 

 describes appearances actually observed by him in the epithelium covering the front 

 of the cornea, which seem to indicate a process of this kind ; but much more extended 

 observations are required to settle the point. I have seen cells with double or divided 

 nuclei in the epithelium of the bladder, but not confined to the deep strata ; on 



the other hand, I have never 



Fig. XXIV. SPINOUS CELLS 

 FROM THE MALPIGHIAN 

 LAYER OF THE HUMAN EPI- 

 DERMIS J ABOUT j^ INCH 

 IN DIAMETKR (after M. 

 Schultze, Virch. Arch. vol. 

 30). 



or produce the smaller cells. 



Fig. XXV. 



been able to perceive indica- 

 tions of division in the deep 

 vertical cells of the epider- 

 mis ; at the same time it is 

 plain that the latter are not 

 mere nuclei imbedded in a 

 blastema ; the nucleus is 

 surrounded by a tolerably 

 well-marked cell-body, which 

 has a deeply denticulate or 

 fringed border at the part 

 turned towards the corium. 



Columnar Epithelium 

 (Cylinderepithelium of 

 Germ. Anat.). In this 

 variety (figs. xxv. and 

 xxvi.), the constituent 



cells are elongated in a direction perpendicular to the surface of the membrane, 

 so as to form short upright columns, which may be of the same thickness 



Fig. XXV. A, COLUMNS OF EPITHELIUM FROM THE 

 INTESTINE MAGNIFIED; B, VIEWED BY THEIR BROAD 



FREE EXTREMITY J C. SEEN IN A TRANSVERSE SECTION 



OF AN INTESTINAL VILLUS (from Henle). 



* Wiirzb. Naturwiss : Zeitschrift, vol. iii. 1862. 



