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fan. Some, such as crangon, when swimming, have the back 
underneath, and the belly upwards. 
Many amphipods swim by means of the contractions of their 
tail, aided by the movements of their feet, and some are forced, 
in consequence of the extreme compression of their body, and 
the very strong curvature of the tail, to remain continually 
couched on one side. 
Although the squillse possess feet adapted for motion, they 
appear to make no more use of them than the macrourous 
Crustacea do of their’s, and their natation appears to be effec- 
tuated principally by the assistance of the ten branchial feet, 
which are placed under a tail less robust and less curved than 
that of the macrouri, but equally terminated by flabelliform 
natatory laminae. 
In the sub-class of the entomostraca, all the animals which 
have numerous soft feet, and furnished with gills, as apus, 
limnadia, and branchipes, advance only by the action of these 
limbs, whose motions are soft and undulating. Daphnis and 
lynceus appear to jump in the water, which has caused the 
first to be sometimes termed aquatic fleas, because their swim- 
ming takes place by violent movements of their ramous an- 
tenna), which are frequently repeated, leaving but few inter- 
vals of complete repose. In cypris, it is the feet, and espe- 
cially the hinder feet, by which the animal advances. 
Among the amphipods, some can leap with considerable 
vigour when they are on land, making use of their tail, folded 
underneath, as a spring. 
The instinct, or mental faculty, of the Crustacea in general, 
when compared with that of other classes, especially the 
insects, appears to be but very moderately developed. The 
crabs and their allied genera, seem to possess it in a higher 
degree than the rest. I hose animals, in fact, exhibit great cun- 
ning, especially in avoiding their enemies: they are then oh- 
