. Beginners' Zoology . Fig. 94.— Hermit Crab,using shell of sea-snailfor a house. the only part cooked being the muscular tail. The crabs tail is small and flat and heid under the body (Fig. 93). Since the limy covering to serve the purpose of protection is not soft enough to be alive and growing, it is evident that the Crustacea are hampered in their growth by their crusty covering. Dur-ing the firstyear the cray-fish sheds itscovering, ormoults threetimes, andonce each yearthereafter. Itgrows very fastfor a few daysjust after moult-ing, while theFig. 95. —Development OF A Crab. covering is s
. Beginners' Zoology . Fig. 94.— Hermit Crab,using shell of sea-snailfor a house. the only part cooked being the muscular tail. The crabs tail is small and flat and heid under the body (Fig. 93). Since the limy covering to serve the purpose of protection is not soft enough to be alive and growing, it is evident that the Crustacea are hampered in their growth by their crusty covering. Dur-ing the firstyear the cray-fish sheds itscovering, ormoults threetimes, andonce each yearthereafter. Itgrows very fastfor a few daysjust after moult-ing, while theFig. 95. —Development OF A Crab. covering is soft a, nauplius just after hatching; b ,c ,d, zoea.; f, megalops; y, adult. ur\(\ extensible Question: Which stage is most like a crayfish? Compare . with metamorphoses of insects. OinCG It IS at. CRUSTACEANS 61 the mercy of birds, fish, and other enemies while in thissoft and defenceless condition, it stays hidden until thecovering hardens. Hence it cannot eat much, but probablyby the absorption of water the tissues grow; that is, the intervening periods, when growth is impossible, itdevelops; that is, the tissues and organs change in structureand become stronger. Soft-shelled crab is a popular dish,but there is no species by that name, this being only a crabjust after moulting which has been found by fishermen inspite of its hiding. General Questions—How do crayfish choose their food? Howlong can they live out of water? Why do their gills remain moistout of water longer than a fish? How do they breathe out ofwater? Are they courageous or cowardly animals? When theylose appendages in fighting or moulting, these are readily reproduced,but an organ moults several times in regaining its size. Have youseen crayfish with one claw smaller than the other? Compare thecray
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