Of what motions are the _eyes_ capable? Touch one of the eyes. The result? Can a crawfish see in all directions? To test this, place a crawfish on a table and try whether you can move to a place where you can see the crawfish without seeing its eyes. What are the advantages and disadvantages of having the eyes on stalks? [Illustration: FIG. 81.--CRAWFISH (dorsal surface).] [Illustration: FIG. 82.] Touch the body and the several appendages of the crawfish. Where does it seem most sensitive to _touch_? Which can reach farther, the antennæ or the big claws? Why are short feelers needed as well as long ones? Make a loud and sudden noise without jarring the crawfish. Is it affected by _sound_? =External Anatomy= (Figs. 81, 82, 83, 84).--Is the body of the crawfish rounded out (convex) everywhere, or is any part of its surface either flat or rounded in (concave)? What _color_ has the crawfish? Is this color of any use to the crawfish? [Illustration: FIG. 83.--LATERAL VIEW OF CRAWFISH.] [Illustration: FIG. 84.--FOURTH ABDOMINAL SEGMENT OF CRAWFISH with swimmeret.] 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 flexible? Why? Is the _covering_ of the body hard or soft? What is the advantage of such a covering? What are its disadvantages? How is the covering modified at the joints to permit motion? =Tail.=--How many joints, or segments, on the tail? (Figs. 81, 83.) Does the hard covering of each segment slip under or over the segment behind it when the abdomen is straight? Does this lessen friction while swimming forward? Is there a pair of _swimmerets_ to each segment of the abdomen? (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 to swimmerets? Do they likewise have the Y-shaped structure? (Fig. 86.) If the swimmerets on the first abdominal segment are large, the specimen is a male. If they are small, it is a female. Which sex is shown in Fig. 82? Fig. 86? =Carapace.=--The covering of the head chest (cephalothorax) is called the carapace. Has it free edges? The _gills_ are on the sides of the body and are covered by the carapace (Fig. 87). The projection in front is called the _rostrum_, meaning beak. Does the rostrum project beyond the eyes? There is a transverse groove across the carapace which may be said to divide the head from the abdomen. Where does this groove end at the sides?