xxiv Introduction 



which are more successfully killed and preserved in 

 alcohol. 



Insects which have been kept dry for some time should 

 be placed in a moist chamber (a tight jar with a little water 

 or a damp sponge in it) for several hours to soften them 

 before being used. 



Crayfishes for class use are easily obtained in many 

 parts of the United States. In the Eastern States, where 

 it is more difficult to get them, they may be bought of the 

 following firms : Middleton, Carman & Co., Fulton Market, 

 New York, N.Y., or Shattuck and Jones, Faneuil Hall 

 Market, Boston, Mass. 



Live lobsters may also be bought of these or other 

 merchants, but the crayfishes are less expensive and more 

 convenient for study. — c. m. w. 



