102 ANIMAL FORMS 



millions are caught each year, and to such an extent has 

 their destruction proceeded that in many places they are 

 well-nigh exterminated. At the present time, however, leg- 

 islation, numerous hatcheries, and a careful study of their 

 life habits is doing much to better matters and inciden- 

 tally to put us in possession of many interesting zoological 

 facts along this line, some of which will be mentioned later. 

 Frequently the prawns, especially the larger ones, and a 

 spiny lobster (Palinurus), are mistaken for crayfishes or 

 lobsters, but they differ from them in the absence of the 

 large grasping claws. 



Along almost any coast some of these animals are to be 

 found, often beautifully colored and harmonizing with the 

 seaweeds among which they live, or so transparent that 

 their internal organization may be distinctly seen. Farther 

 out at sea other species swim in incredible numbers, feed- 

 ing upon minute organisms, and in turn fed upon by numer- 

 ous fishes and whales ; and, especially on the Pacific coast, 

 shrimp-fishing is an important industry. 



103. The hermit-crabs. The last of these long-tailed 

 decapods is the interesting group of the hermit-crabs, 

 which occur in various situations in the sea. In early life 

 they take possession of the empty shell of some snail, and 

 the protected abdomen becomes soft and flabby, while the 

 appendages in this region almost completely disappear. 

 The front part of the body, on the other hand, continually 

 grows in firmness and strength, and is admirably adapted 

 for the continual warfare which these forms wage among 

 themselves. As growth proceeds the necessity arises for a 

 larger shell, and the crab goes "house-hunting" among the 

 empty shells along the shore, or it may forcibly extract the 

 snail or other hermit from the home which strikes its fancy. 



Many of the hermit-crabs enjoy immunity from the 

 attacks of their belligerent relatives by allowing various 

 hydroids to grow upon their homes. Others attach sea- 

 anemones to their shells or to one of their large claws, 



