34 



THE FROG 



clean and dry both slide and cover glass. Do not lift the microscope 

 by the tube; if there is no handle, use the base. 



B. Tissues 

 Exercise 28. — Squamous Epithelium. 



(a) The outermost layer of the frog's skin which is composed of 

 squamous epithelium is sloughed off when living frogs are confined 

 in a small aquarium. It can, also, be obtained from the liquid in a 

 jar of preserved specimens. The outer layer of your own skin is con- 

 tinually sloughing off in a similar manner except that it falls away 

 in microscopic dry particles. 



c&JI meTTtbranc' 

 nz^cJear membrane 



?zz^c/eoJzi3 



fat 



CoJqi eJement^ - ■% 

 cJtondrioso/77es _^. 



^ cenlrh?e' 



cenirospherC' 



- chromatin 

 -fa? 



- - ^ecreF/o!? franiih 



— Yesic/e^ 



Fig. 26. — A composite animal cell in the vegetative phase; diagrammatic. 



(b) Place a small piece of the outer layer of the frog's skin in a 

 drop of water on a clean slide. Spread out the filmy mass without 

 tearing, add a cover glass, and focus on the mass with the low-power 

 objective in position. Adjust the iris diaphragm so that you can see 

 the cell outlines clearly. How many sides do the cells have? How 

 are they arranged? Observe with the high-power objective and note 

 that each cell has a distinct nucleus surrounded by a cytosome (c/. 

 Fig. 2G). Two or more layers of cells may be seen in some places. 



