20 ANIMAL ACTIVITIES. 
preserved in the same way, but they make better speci- 
mens for study, if preserved in formalin or alcohol. 
Shells and Bones. To remove snails from their 
shells put them in hot water for a few moments. The 
shells may then be cleaned and dried. To clean fleshy 
matter from a skeleton like that of the starfish use a 
dilute solution of caustic potash. Sometimes it is well 
to boil specimens in that liquid. The bones of larger 
animals can be cleaned enough for class use by simply 
boiling and removing the fleshy parts. When such 
specimens are to be kept for a long time more care is 
needed, and books containing more specific directions 
should be consulted. Part C of Bulletin No. 39, pre- 
viously mentioned, is helpful. 
MATERIAL FOR WINTER AND SPRING. 
The preceding directions are for classes which begin 
Zodlogy in the fall. When the work begins in the 
spring the order of 
work should be modi- 
fied somewhat, begin- 
ning with Protozoa and 
reaching the subject of 
Arthropoda after warm 
weather brings the 
living specimens again 
within easy reach. 
Even in winter much 
material can be pro- 
cured by the pupils for 
their study. 
Cockroaches. Cock- 
roaches were originally 
southern insects. They 
are now distributed 
almost everywhere, and 
are fairly abundant even 
in cold weather. They are most easily collected at 
Fic. 29.—A Cockroach. 
