56 LABORATORY EXERCISES. 



28. CIRCULATION OF THE BLOOD IN THE 

 TAIL OF THE TADPOLE. (Dem.) 



Cut a hole a half-inch square near the end of a piece of thin board 

 three inches long and one inch wide ; glue a thin cover-glass over the 

 hole. Cover the rest of the piece of wood with absorbent cotton 

 soaked in water. Lay a live tadpole on the cotton, placing the tip 

 of the tail on the cover-glass. Lay a cover-glass on top of the tail, 

 and fasten cheese-cloth over the animal to keep it in place. Keep a 

 plentiful supply of moisture about the animal, by allowing the end 

 of the strip of cloth to dip into a dish of water. Examine the tip of 

 the tail with a compound microscope magnifying about 75 diameters 



. i. At the highest focus note the epithelial cells 

 forming the outside layer of the body 

 covering. What is their shape? 



2. What is the shape of the dark pigment-cells 



seen just beneath the epithelial cells? 



3. Focus still lower and study the flow of the 



blood in the small capillaries. 



a. Is the current steady in all the blood- 



vessels which you see? 



b. Do the red corpuscles alter in shape 



as they move along? 



c. Can you distinguish any colorless cor- 



puscles? 



d. Draw a small area of the tail, repre- 



senting the course of the capilla- 

 ries. Indicate by arrows the 

 course of the blood in each capil- 

 lary. 



NOTE. If tadpoles cannot be obtained, the web of a frog's foot 

 may be examined after confining the frog on a larger piece of board 

 than that described above. 



