25* ELEMENTARY BIOLOGY. [CHAP. 



ver; according to the amount of staining a 

 nucleus may or may not be rendered conspi- 

 cuous in each cell. 



Here and there in good specimens, rings 

 of smaller and more deeply stained cells will 

 be seen surrounding minute apertures (sto- 

 mata). 



I. Columnar epithelium. Scrape gently the inner 

 surface of the mucous membrane of the intes- 

 tine of a frog which has been preserved in 

 Miiller's fluid; mount the detached fragments 

 in water and examine with a high power. 



a. Numerous elongated cells, flat at one end 

 and somewhat pointed at the other, will be 

 seen. Each has a well-marked oval nucleus. 



J3. These cells may be seen in situ if a thin sec- 

 tion of the hardened mucous membrane of 

 the intestine or stomach be examined. They 

 are closely applied and arranged in a single 

 layer. 



c. Ciliated epithelium. Snip off a bit of the mucous 

 membrane from the tongue of a recently killed 

 frog with a sharp pair of scissors : mount the 

 bit in 07 5^- sol. of sodic chloride, avoiding 

 pressure, and examine with a high microscopic 

 power. 



a. Note the shimmering appearance along its 

 free edge, produced by the rapidly moving 

 cilia; as the cilia begin to die and their 

 movement slackens, individual ones can be 

 seen. 



