THE EARTHWORM I29 



(8) Put a living earthworm in water. Does it seem 

 to be comfortable? What vital process is cut off while it 

 is in the water? Did you find any provision for breathing 

 in the animal? Do you think it breathes? Take it out of 

 the water and see if it revives. Can the earthworm breathe 

 in dry air? Since the blood vessels appear to be near the 

 surface, can you suggest its method of breathing? Why 

 do so many earthworms come to the surface after a rain? 

 Describe the process of respiration. 



(9) The anatomy of the earthworm may be better un- 

 derstood by studying a cross section. Use a specimen that 

 has been hardened in ninety-five per cent, alcohol. Cut a 

 piece about two inches long from the center of the worm, 

 and wash out the intestine so that it may be further studied. 

 Cross sections of this piece may be made thin enough for 

 class study by holding the piece between the thumb and 

 forefinger of the left hand and cutting sections with a 

 razor. Examine the body wall. The cuticle is a thin chiti- 

 nous layer of an iridescent luster. Below this is the epi- 

 dermis, which consists of a single layer of cells elongated 

 in the vertical direction. Below this is a layer of connective 

 tissue, the dermis. This can scarcely be distinguished. The 

 next layer of the body wall is the circular muscles. The 

 layer within the circular muscles is the longitudinal mus- 

 cles. These are featherlike, and stand at right angles to 

 the circular muscles. They are interrupted, and appear to 

 be divided into bundles. How many? By examining two 

 or three cross sections the exact position and arrangement 

 of the setae may be made out. Can you see where the 

 nephridia open to the exterior ? Study- the nephridia and 

 see if you can make any clear statement about their shape 



STU. IN ZOOL. — 9 



