54 



BEGINNERS' ZOOLOGY 



Fig. 83. —Lateral view of Crawfish. 



What colour has the crayfish? Is this colour of any use to 

 the crawfish ? 



Make out the two distinct regions or divisions of the body 

 (Fig. 81). The anterior (front) region is called the head- 

 chest or cephalothorax, and the posterior (rear) region is 



called the tail. 

 Which region is 

 larger ? Why ? 

 Which is flex- 

 ible? Why? 



Is the covering 

 of the body hard 

 or soft ? What 

 is the advantage of such a covering ? What are its dis- 

 advantages ? How is the covering modified at the joints 

 to permit motion ? 



Tail. — How many joints, or segments, of the tail ? (Figs. 

 81, 83.) Does the hard covering of each segment slip 

 under or over the segment behind it when 

 the tail is straight ? Does this lessen 

 friction while swimming forward ? 



Is there a pair of swimmerets to each 

 segment of the tail? (Figs. 82, 86.) 

 Notice that each swimmeret has a main 

 stalk (protopod), an outer branch (exopod), 

 and an inner branch (endopod) (Fig. 84). 

 Are the stalk and the branches each in 

 one piece or jointed ? The middle part of the tail fin is 

 called the telson. By finding the position of the vent, 

 decide whether the food tube goes into the telson 

 (Fig. 82). Should it be called an abdominal segment. 

 Are the side pieces of the tail fin attached to the telson 

 or to the sixth segment ? Do these side pieces correspond 



Fig. 84. — 

 Fourth Abdo- 

 minal Segment 

 of Crawfish 

 with swimmeret. 



