THE CRUSTACEANS. 303 
has, by its rapid movements, acquired the name of the horseman ; 
but it may be doubted if its pace be equal to that of a horse. 
The Large-clawed Porcellana (Porcellana platycheles) is a bad 
swimmer ; by certain movements of its abdomen it can just manage 
to come up from the water and again descend ; but usually it lies 
crouched under a rock for months together, its long antenne 
stretched out to examine any object which may be in its immediate 
neighbourhood. Its jaw-claws are constantly being thrown out, 
and pulled in towards its mouth. These claws are like reaping- 
hooks; they are formed of five joints, and on their inner edge are 
furnished with rows of stiff bristles; the microscope shows that 
these bristles themselves are provided with fine hairs standing out 
THE COMMON SHRIMP. 
(Crangon vulgaris.) 
perpendicularly from their sides. In the movements of retraction, 
these numerous filaments cross each other so intimately, that they 
form a minute trellis-work, by which all the animalcules in the 
water are brought into the mouth of the crab, and when the claws 
are thrown forward, all the crab ejects is swept away from its 
neighbourhood ; by this means the creature can obtain the nourish- 
ment necessary for its existence without changing its place. 
Shrimps have at the extremity of their first pair of claws an 
appendage not unlike a rake. The teeth of this apparatus are fine 
hairs standing out of the membrane perpendicularly. The creature 
by this organ gathers together the minute particles which the next 
pair of claws passes on to the mouth. This rake also serves the 
purpose of a brush with. which the little crustacean cleanses its 
bent claws and the lobes of its tail. When busy with its toilet 
the shrimp stands erect on its long claws, and its tail is bent under 
its body, in order to permit the first pair of claws to brush it. 
