. Beginners' Zoology . Fig. 82. crayfish without seeing its eyes. What are the advantagesand disadvantages of having the eyes on stalks ? Touch the body and the several appendages of thecrayfish. Where does it seem most sensitive to touch ?Which can reach farther, the antennae or the big claws?Why are short feelers needed as well as long ones ? Make a loud and sudden noise without jarring the cray-fish. Is it affected by sound? External Anatomy (Figs. 81, 82, 83, 84). — Is the body ofthe crayfish rounded out (convex) everywhere, or is anypart of its surface either flat or rounded in (concave)
. Beginners' Zoology . Fig. 82. crayfish without seeing its eyes. What are the advantagesand disadvantages of having the eyes on stalks ? Touch the body and the several appendages of thecrayfish. Where does it seem most sensitive to touch ?Which can reach farther, the antennae or the big claws?Why are short feelers needed as well as long ones ? Make a loud and sudden noise without jarring the cray-fish. Is it affected by sound? External Anatomy (Figs. 81, 82, 83, 84). — Is the body ofthe crayfish rounded out (convex) everywhere, or is anypart of its surface either flat or rounded in (concave) ? 54 BEGINNERS ZOOLOGY What colour has the crayfish? Is this colour of any use tothe crayfish? Make out the two distinct regions or divisions of the body(Fig, 8i). The anterior (front) region is called the head-chest or cephalothorax, and the posterior (rear) region is called the region islarger ? Why ?Which is flex-ible ? Why ? Is the covering of the body hard or soft ? What What are its dis-. Lateral view of Crayfish. Fig. 83. is the advantage of such a covering ? advantages ? How is the covering modified at the joints to permit motion ? Tail. — How many joints, or segments, of the tail ? (, 83.) Does the hard covering of each segment slipunder or over the segment behind it whenthe tail is straight ? Does this lessenfriction while swimming forward ? Is there a pair of szviniviercts to eachsegment of the tail? (Figs. 82, Z6^Notice that each swimmeret has a mainstalk (protopod), an outer branch (exopod),and an inner branch (endopod) (Fig. 84).Are the stalk and the branches each inone piece or jointed ? The middle part of the tail fin iscalled the telson. By finding the position of the vent,decide w^hether the food tube goes into the telson(Fig. 82). Should it be called an abdominal segment?Are the side pieces of the tail fin attachedto the telsonor to the sixth segment ? Do these side pieces correspond
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