ADAPTATION TO SURROUNDINGS 75 



the animal is at rest ; when it is in motion ? How much 

 territory can the two pairs guard ? 



9. Touch the eyes. Compare their sensitiveness with 

 that of your own eyes. What movements can the eyes 

 perform .' How are they protected ? What range of terri- 

 tory can they guard ? 



10. What other senses, if any, do you think a crayfish 

 has ? Why do you think so ? 



11. Early in the spring crayfishes may be found carry- 

 ing eggs or young. If such a specimen is at hand, notice 

 where and how the eggs or young are attached. How 

 many are there .■' How are they cared for .■• Can the 

 young crayfish let go ? If removed, can they attach them- 

 selves again .-' How much care does the mother give 

 them when they are removed .■• 



Morphology of a Crayfish 

 Definitions. 



Cephalo-thorax, the anterior half of the body, divided into 

 the head and the thorax. 



Cervical groove, the groove dividing the head from the 

 thorax. 



Abdomen, the posterior half of the body, consisting of a 

 number of somites. 



Note. — The central part of the tail fin is usually included as a 

 somite. 



Carapace, the continuous shell-like portion of the exo- 

 skeleton covering the cephalo-thorax. 



Rostrum, the sharp projection of the carapace at the 

 anterior end. 



Gill chamber, a pocket on each side of the thorax, cov- 

 ered by a flap of the carapace. 



