186 THE OCEAN. 
the hindmost pair have the last joint flattened out 
into a thin but broad oval plate, the edge of which 
is thickly fringed with fine hairs. This structure is 
exactly parallel to that by which the foot of a perch- 
ing bird is modified into the foot of a swimming 
bird, the surface being dilated into a broad web; or 
to the wide fringe by which the hind feet of a water- 
beetle are made such powerful oars; the flattened 
joint in the present case becoming a paddle, by the 
- stroke of which a rapid motion is obtained through 
the water. These Swimming Crabs are very vora- 
cious, preying upon the little shrimps that are nume- 
rous about the weed, which they pursue and seize 
with their pincers. Sometimes the Crab remains 
at rest, but vigilant, until a shrimp swims within 
reach, when he grasps it with great quickness, and 
proceeds to devour it by degrees. In doing this, 
he holds it fast by one claw, while with the other 
he picks off very daintily the legs and other mem- 
bers of his prey, putting them bit by bit into his 
mouth, until nothing remains but the tail, which he 
rejects. 
The weed is usually the resort of several small 
species of fishes, which doubtless congregate about 
it for the sake of the minute Crustacea that are so 
abundant. Among them I have found a very in- 
teresting little species of Toad-fish (Antennarius), 
whose pectoral and ventral fins project so far from 
the surface of the body as to expose the joint, and 
thus take the form of the feet of a quadruped. It 
uses these members actually as feet, crawling and 
pushing its way among the tangled weed by means 
