24 PRACTICAL ZOOLOGY. 



THE CRAYFISH. 



Get a number of live crayfishes. They are usually to 

 be found hidden under stones in the shallow water of 

 creeks. Put into alcohol at least three for each student. 

 Keep some of them alive in an aquarium a large pan 

 will serve, though the vertical sides of a regular aquarium 

 render it easier to watch the movements of these and 

 other aquatic animals. Let each student have a live cray- 

 fish in a fruit-jar. Examine from above, from the side, 

 and from beneath. How many legs does the crayfish use 

 in walking ? Frighten the crayfish by suddenly thrusting 

 a pencil at it ; how does it effect such rapid locomotion ? 

 Touch one of the eyes with the pencil; what follows? 

 Move the pencil slowly toward one of the large claws. 

 What does the crayfish eat, and how does it eat ? What 

 are its habits ? 



The crayfish and lobster are so nearly alike that these 

 directions, though written for the crayfish, will serve 

 fairly well for the latter. Use crayfishes that have been 

 a short time in alcohol. If lobsters are used, get unboiled 

 specimens. 



EXTERNAL PARTS OF THE CRAYFISH. 



1. The united head and thorax are called the cephalo- 

 thorax. 



2. The continuous covering of the two is the carapace. 

 The projection of the carapace, above and between 

 the eyes, is the rostrum. 



3. The hinder, flexible part of the body is the abdomen. 

 Count its rings, or segments. Bend (flex) the ab- 

 domen, and straighten (extend) it repeatedly, observ- 



