THE EARTHWORM 173 



prostomial lobe is the most sensitive part of the body; here 

 the sense cells are most abundant and here the nerve supply is 

 the largest; Fig. 79. 



LABORATORY WORK ON THE EARTHWORM 



Only large specimens should be used. These can be purchased from 

 dealers in natural history supplies or they may be collected by searching 

 with a lantern on a dark night, when they may be found stretched out 

 on the ground and thus readily collected. A little care and experience 

 is needed to do this without disturbing them, for they are very sensitive 

 to the slightest jar and quickly retreat into their burrows. 



The specimens should first be studied alive, if possible, to see the con- 

 traction of the dorsal blood vessel and the contractions of the body in 

 locomotion. The setae may be felt by drawing the body gently through 

 the fingers, and they can be examined under a lens. 



If the worms are to be dissected, or preserved for future use, they should 

 be treated as follows: Place the worms in a shallow dish with wet filter 

 paper torn into shreds. The animals will swallow it and as it passes 

 through the alimentary canal it will carry the dirt from the canal. This 

 part of the process is not necessary unless microscopic sections are to be 

 made. If they are to be kept simply for dissection, they can be preserved 

 at once as follows: 



Place a number of worms in a shallow dish with just water enough 

 to cover them. Add a few drops of alcohol, and, after a few moments, 

 add a little more. Continue adding the alcohol gradually until the ani- 

 mals have become motionless and relaxed. This process should take at 

 least two hours. Then transfer them to a large shallow dish containing 

 50% alcohol, straightening the animals out, and laying them side by side. 

 After an hour replace the 50% alcohol with 70%; after a few hours change 

 again to a fresh lot of 70% alcohol. Finally the animals are to be placed 

 in 90% alcohol. It is important to keep them straight in this final hard- 

 ening fluid, and this may be done by laying them out on rather stiff paper, 

 without touching each other, and rolling them, putting about a dozen in 

 each roll. This will hold them in proper shape, and the rolls may be 

 stored in tall jars and will keep indefinitely. 



Animals so preserved will serve either for microscopic sections or for 

 dissection. Sections should be made by the instructor and, after stain- 

 ing, should be mounted and furnished the student for study. 



For dissection, the animal should be placed, under water, in a tray 

 containing dissecting wax. The anterior end is pinned down and then, 



