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)? 5
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. Fig. 83.—Lateral view of Crawfish. What colour has the crayfish? Is this colour of any use tothe crawfish ? Make out the two distinct regions or divisiojis of the body(Fig. 81). The anterior (front) region is called the head-chest or cephalothorax, and the posterior (rear) region is called the region Why ?Which is flex-ible? Why? Is the coveringof the body hardor soft ? Whatis the advantage of such a covering ? What are its dis-advantages ? How is the covering modified at the jointsto permit motion ? Tail. — How many joints, or segments, of the tail ? (, 83.) Does the hard covering of each segment sUpunder or over the segment behind it whenthe tail is straight ? Does this lessenfriction while swimming forward ? Is there a pair of swinivierets 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
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectzoology, bookyear1921
