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 Zoéa and the Mega- 
lops. So little do these resemble the adult that originally they 
were classed as distinct 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 zoéa stage. 
From this it changes directly to Megalops ; the Zoéa, 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 alge, 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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