CRABS 273 



Crabs, like other crustaceans, are scavengers, living on dead ani- 

 mal matter ; but the land species are also vegetarian in diet. They 

 are great fighters, but are also wily, often averting danger by 

 resorting to stratagem. They are an interesting and curious 

 group, as they possess a good degree of intelligence and have 

 amusing habits. 



From the time they leave the egg until they attain the adult 

 form they pass through several complete and singular metamor- 

 phoses. The most marked forms are called the Zoea and the Mega- 

 lops. So little do these resemble the adult that originally they 

 were classed as distrnct genera far removed from the one to which 

 they really belong. After the larva has moulted several times it 

 appears as in the illustration on page 248 the last zoea stage. 

 From this it changes directly to Megalops ; the Zoe'a, seeming to be 

 attacked with violent convulsions, wriggles out of its skin a full 

 Megalops (page 248). The animal then has enormous eyes, an ex- 

 tended abdomen, an elongated carapace, and swimming-legs. This 

 stage is a short one, and at the first moulting changes to a form 

 nearly approaching the adult. From this time they grow by 

 shedding the shell at certain periods. This shedding is supposed 

 to occur twice each summer until they have reached full growth, 

 after which it is probable that they do not again moult ; for often 

 they are found with extraneous organisms, such as barnacles and 

 sponges, upon them, of a size that must have required a consider- 

 able period of time for growth. The sexes of the same species 

 sometimes differ so much that it is difficult to classify them. 

 Even naturalists have been led into the error of assigning the 

 male and female to separate species. 



The front side margins of the carapace in many crabs are edged 

 with a row of teeth or with spines, which vary in number and 

 character in different species. In the spider-crabs the whole sur- 

 face of the carapace is generally studded with tubercles, spines, 

 and stiff hairs of a peculiar character. This armature is for pro- 

 tective purposes, and is often used to secure foreign bodies, such 

 as algae, hydroids, and polyzoans, which the crabs place upon their 

 backs to disguise themselves. The burrowing crabs are usually 

 smooth. When in motion the crab moves sideways, using the legs 



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