I.] THE FROG. 125 



of a frog, and mount the detached fragments in 

 water. Examine with a high power. 



a. Numerous elongated cells will be seen, some- 

 what resembling those of the ciliated epithelium 

 in shape, but more uniform in size. Each is 

 flat at one end and somewhat pointed at the 

 other, and has a well-marked oval nucleus. 

 Not unfrequently aggregates of them may be 

 seen : look for such, and note that the cells 

 are closely applied and arranged in a single 

 layer. 



(3. Goblet cells ; scattered among a ; characterised 

 by the presence of a watery-looking globule 

 (mucus drop} which distends the free end or 

 greater part of the cell body. Note the position 

 of the nucleus. 



c. Scaly or tesselated epithelium. Open the body 

 cavity of a recently-killed frog ; carefully remove 

 the viscera and lay bare the cisterna magna. Cut 

 away its thin wall as carefully as possible, taking 

 great care not to drag or pull it. Place the frag- 

 ment in 0-5$ solution of silver nitrate for three 

 minutes or longer : then remove, wash well in 

 distilled water, and finally leave the specimen in 

 the same fully exposed to the sunlight. When it 

 has assumed a well-marked brown colour stain 

 with eosin or haematoxylin and examine with a 

 high power. 



a. The matrix (intercellular cementing substance); 

 rendered highly conspicuous as a network of 

 black lines, irregularly disposed on the free 

 surfaces of the mesentery. 



