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HISTORY OF BRITISH CRUSTACEA. 
of foot-jaws of two joints, and not like a sucking-disc. 
Segments of thorax uncovered. Body more or less oval, 
depressed. Eyes two, close together : in the living animal, 
of a red colour, and slightly projecting. 
The species of this family are found on various fishes in 
the sea. They adhere to the body among the scales, being 
attached by their foot-jaws. They can move to any part of 
the fish. They die soon after the fish is taken from the 
water. There seems to be some doubt as yet about their 
food. The most minute observers seem to think that it is 
chiefly, if not wholly, on the mucous juices of the fishes 
that they subsist, those juices which cover the body of the 
fish, and for secreting which in abundance there are, in most 
fishes, a series of particular pores. The fishes on which they 
are found are generally weak and diseased. The young 
Caligida, when first hatched, are very different in appear- 
ance from the adult : they closely resemble the young of the 
Cyclopula , and undergo, like them, a number of changes of 
skin before they assume the completely-developed form of 
the parent. 
