472 



BIOLOGY FOR BEGINNERS 



fish bait, and obtains from the cuttle fish the true " sepia," a brown 

 ink-like pigment which the animal squirts out to hide itself when 

 attacked. The " cuttle bone " familiar in the canary cage is the 

 internal shell of this same mollusc. 



Crustacea. The larger crustaceans, lobsters, crabs, shrimps, 

 and prawns are valuable sources of food to man; the smaller 

 forms are equally valuable as food for fish, and all are useful 

 scavengers. Of all these the lobster is most valuable. From twenty 

 to thirty million are annually caught along the coasts of New 

 England and Canada and the business is carefully regulated by 



FIG. 151. The giant squid, Ommatostrephes calif ornica. From specimen 

 with body, exclusive of tentacles, four feet long, thrown by waves on 

 the shore of the Bay of Monterey. From Kellogg. 



law to prevent their destruction by over fishing. " Soft shell " 

 crabs are merely the ordinary blue crabs, taken just after moulting 

 and before their new shells have formed. 



Barnacles are curious crustaceans which attach themselves to 

 rocks, piles and even to the bodies of whales and bottoms of ships. 

 In the latter place they interfere with easy sailing and have to be 

 removed. 



Acerata. Spiders as a whole are distinctly beneficial because 

 of their destruction of flies and other insects; their bite is seldom 

 serious to man, though some large tropical kinds can kill small 

 birds. Scorpions are found in Southern United States and tropical 



