112 CRUSTACEANS. 



situations. Some live in holes in the soil ; others do not. 

 Some of the former build chimneys of mud about the 

 entrance to their holes ; others do not. Some live at the 

 surface of ponds, on the floating or submerged leaves of 

 aquatic plants. 



In many localities throughout the interior the species 

 that live in holes are very abundant. The following 

 questions suggested for field study of their habits may 

 be useful : 



1. What are their hours of activity ? 



2. At what depth of water do you find them ? 



3. Do they live singly, in pairs, or in communities ? 



4. Do those that live in holes make the holes for them- 

 selves ? Are their holes ever found sheltered beneath 

 stones and tree roots ? 



5. What is the general shape, size, and direction of 

 these holes, and at what level do they terminate below ? 



6. In such as build chimneys, how is the chimney con- 

 structed? Is the chimney ever found plugged up with 

 mud, except in very dry weather ? 



7. How many species do you find, and what are the 

 haunts of each ? 



In winter, numbers of certain species may often be found 

 huddled together under the sheltering edge of some loose 

 stone in the bed of a creek. Where the holes of other 

 species are common in the banks of brooks, they may be 

 dug out when the ground is not frozen. 



Habits. Live specimens may be kept for a long time 

 in any sort of aquarium supplied with food. They will 

 eat snails and insects greedily, and will live on almost any 

 kind of flesh. 



Startle a crawfish at rest upon the mud, and observe the 

 cloud it raises in the water, behind which to escape. 



Watch a crawfish walking about in an aquarium, and 



