XIII.] THE FEOG. 243 



6. Columnar epithelium. Scrape gently the inner 

 surface of the mucous membrane of the intestine 

 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. 



/S. These cells may be seen in situ if a thin section 

 of the mucous membrane of the intestine or 

 stomach be examined. They are closely ap- 

 plied 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 0*7o^ sol. of sodic chloride, avoiding pres- 

 sure, 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. 



/3. Scrape gently, with a scalpel, one of the pro- 

 minences in the roof of the frog's mouth beneath 

 the eye-balls : mount the scrapings in 075 salt 

 solution and examine with i objective for in- 

 dividual ciliated cells ; note their roundish form, 

 granular protoplasm and nucleus, and the group 

 of cilia borne on one end ; stain with iodine. 



b. Cartilage. 



1. Dissect out carefully the omosternal or xiphisternal 

 cartilage of a recently killed frog; mount in 0'75g 

 sodic chloride solution and examine with :^ or ^ obj. 



16-2 



