DIRECTIONS FOE LABORATORY WORK 771 



(6) Study in physiologic salt solution ciliated cells scraped from 

 the roof of the mouth of a pithed frog. Observe the activity of the long 

 cilia. (An equally instructive preparation can be obtained from the 

 gills of a living oyster or clam.) Sketch (43). 



(7) Pigmented cell. Sketch (44) a few pigmented cells (cubic) 

 from the pigment layer of the retina or the iris, from a stained section 

 of the eye. 



(8) Flagellate cell. Sketch (45) a spermatozoon from a stained 

 section of a mammalian testis; or from a preserved specimen of human 

 semen. 



(9) Neuroepithelium. Sketch (46) a few cells from the bacillary 

 (rod and cone cell) layer of the retina, in a stained section of the eye. 



(D) CUBIC. 



Sketch (47) a small extent of cubic epithelium in the loop of the 

 uriniferous tubule, from a stained section of the kidney. 



II. Complex (Stratified) Epithelium. 



(1) Squamous. Sketch (48) portion of the mucosa of the esophagus, 

 from a stained section. (A stained section of cornea or of thin skin is 

 almost equally favorable.) Note the intercellular bridges between cells 

 of the middle layers, especially prominent in skin. 



(2) Sketch (49) the several types of cells included in a stratified 

 squamous epithelium, from a macerated preparation of the esophageal 

 mucosa. 



(3) Pseudostratified columnar. (This type is almost invariably cil- 

 iated exceptions, larger ducts of glands, portion of ductus deferens.) 

 Sketch (50) small extent of mucosa of trachea or bronchus, from a 

 stained section. (This type of epithelium is sometimes erroneously re- 

 ferred to as 'stratified columnar'. True stratified columnar epithelium 

 is of .meagre and variable occurrence, sometimes as patches among the 

 pseudostratified epithelium. Stratified columnar epithelium occurs in 

 the mucosa of the intermediate portion of the male urethra.) 



(4) Transitional. Study carefully and draw (51) a small area of 

 the lining epithelium of the bladder or ureter (preferably in the slightly 

 distended condition) from a stained section. 



(5) Sketch (52) the several characteristic types of cells which con- 

 stitute a transitional epithelium from a dissociated preparation of the 

 bladder mucosa. 



