VERTEBRATE EPITHELIAL TISSUES 1 



A. Squamous Epithelium 



1. The flattened, or squamous, type of epithelial cells may be observed 

 in the outer layers of frog skin which are continually being sloughed off. 

 Secure some of this shed tissue unstained. Mount and examine under the 

 microscope. Note the large surface area of these cells as compared with 

 their thickness. Add a few drops of stain, such, for example, as acetic 

 carmine. Reexamine and note the differentiation of the various cellular 

 structures. Draw to show the structure as observed. 



2. This same type of epithelial tissue, but with the cells usually more or 

 less separated from each other, may also be obtained by gently scraping 

 the inside of your cheek with a clean, blunt instrument, such as the handle 

 of your scalpel. Secure some cells in this manner. Mount, stain, and 

 examine as noted above. Draw to show the structure as observed. 



B. Stratified Epithelium 



3. Examine a prepared, transverse section of frog skin and note that 

 the outer region, or epidermis, which develops from the ectoderm, is 

 composed of several layers of epithelial cells, ranging in shape, by gradual 

 transition, from the squamous type on the upper surface, such as was 

 noted in paragraph 1, to the tubular shaped cells of the columnar epithe- 

 lium lying next to the dermis. Draw to show the different types of epi- 

 thelial cells observed in the various layers of the epidermis. 



C. Ciliated Epithelium 



4. Secure a small piece of the living mucous membrane from the roof 

 of the mouth of an anaesthetized Frog. Place the tissue in normal salt 

 solution and tear it apart with dissecting needles in such a way as to 

 secure tiny bits of the lining layer containing numerous ciliated epithelial 

 cells. With a pipette pick up some of these bits of tissue. Mount and 

 examine with low and high power and note the vigorous ciliary action on 

 the outer edge of these cone-shaped cells. Stain the preparation. Re- 

 examine and then draw to show the structure as observed. 



D. Secretory Epithelium 



5. Examine a prepared transverse section of frog intestine under the 

 microscope. Focus on the inner epithelial layer (mucosa) which originally 

 develops from the endoderm and which forms the functional digestive and 

 absorptive tissue of the intestine. Study with the high power and note 

 numerous elongated secretory, or glandular, cells which are structurally 

 characterized by the presence of an oval-shaped secreting area near the 

 distal end. Draw a portion of the mucosa showing these cells. 



i B. pp. 167-169. 

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