MAMMALIA— PHYSIOLOGY 



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constantly being worn off and replaced. Cubical epithelium is 

 found in the bronchioles of the lungs and in the ducts of certain 

 glands of the digestive system. Columnar epithelium is found 

 lining the alimentary canal of vertebrates and a peculiar type of 

 " ciliated " columnar cell is commonly found in the trachea and 

 bronchi and lining the oviduct and the central canal of the spinal 

 cord. Glandular epithelium consists of epithelial cells so differen- 



1A 



2A 



Fig. 238. Diagram illustrating different forms of glands. Upper row, tubular 

 glands; /, 2, and J, simple tubular glands; 4, compound tubular gland. Lower row, 

 alveolar glands; /a, 2a, and Ja, simple alveolar glands; 4a, compound alveolar gland. 

 (From Bailey's Histology. Courtesy of Wm. Wood and Co.) 



tiated as to be capable of forming compounds given off as secretions. 

 The simplest type of glandular cell is the unicellular gland called the 

 " goblet " cell. This type of mucus-secreting cell is found in the 

 hypodermis of the earth worm and occurs also in the intestines of 

 vertebrates. N euro- epithelium is found lining some of the ven- 

 tricles of the vertebrate brain. Certain cells are aggregated into 

 end organs of special sense. The sensory cells are spindle-like with 

 hair-like processes extending as fine fibers at the inner end and 

 establishing connection with the nerve. Ordinarily these cells are 

 surrounded by supporting sustentacular cells. Germinal or repro- 

 ductive epithelium is found in the gonads. The sexual cells arise 



