58 LECTURE II. 



other, and nothing at all is found between them. The 

 same is the case in many places with the scaly or pave- 

 ment-epithelium (Fig. 16). These forms are evidently 

 in a great measure due to pressure. For all the elements 

 of a cellular tissue to possess perfect regularity of form, it 

 is requisite that they should all grow in a perfectly uni- 

 form manner, and simultaneously. If their development 

 takes place under circumstances such that less resistance 

 is offered in one direction, it then may come to pass 

 that, as in the case of columnar or cylindrical epithelium, 

 the cells will shoot out in this one direction and become 

 very long, whilst in the other direction they remain very 



narrow. But even one of 

 these cells, when seen in 

 transverse section, will pre- 

 ent an hex agonal shape, 

 and if we look down upon 

 the free surface of cylindri- 

 cal epithelium, we see in it, 

 too, regularly polygonal forms (Fig. 14, b). 



Contrasting with these, singularly irregular forms are 

 met with in places where the cells shoot up in an irregu- 

 lar manner, and accordingly they are found with remark- 

 able constancy on the surface of the urinary passages, in 

 their whole extent from the calyces of the kidneys down 

 to the urethra. In all these parts it is very common to 

 meet with instances in which a cell is round at one end, 

 whilst at the other it terminates in a point, or where it 

 exhibits the appearance of a somewhat thick spindle, or is 



Fig. 14. Columnar or cylindrical epithelium from the gall-bladder, a. Four con- 

 tiguous cells seen in profile, each with a nucleus and nucleolus, their contents 

 slightly marked with longitudinal striae ; along the free (upper) edge, a thickish 

 border, marked with fine, radiated lines, b. Similar cells, with their free (upper, 

 outer) surface seen obliquely, so as to show the hexagonal form of a transverse 

 section, and their thick border, c. Cells altered by imbibition, somewhat swollen 

 up and with the upper border split into fibrils. 



