CRABS AND SHRIMPS. 
207 
interesting light on the office of the organs last-named.*' 
Any one may easily identify them in the Lobster or Prawn. 
Take the latter. On each side of the long sword-like and 
spiny beak that projects above the head, there is an organ 
consisting of three stout joints, at the tip of which are 
three threads, of which two arc of great length, and formed 
of numberless rings, and the third is short. These organs, 
then, constitute the inner pair of antennae. Below these 
there is a pair somewhat similar, but they consist each of 
five joints, and one long thread, with a large flat plate on 
each side. These are the outer antennee. The former are 
the organs of hearing, the latter thoso of smelling. 
In the living animal, the inner antenruo are always car- 
ried in an elevated posture, and are continually flirted to 
and fro with a rapid jerking motion that is very peculiar, 
striking the water every instant. It is very conspicuous in 
the Crabs, from the shortness of the organs in question. 
When next our readers, gazing on the teuants of those 
wonderful marine tanks at the Zoological Gardens in the 
Regent’s Park, see a Crab tapping the surrounding water, 
and, as it were, feeling it— they may understand that 
he is trying it for the vibrations of sound : it is the action 
of vigilant listening, which never relaxes its guard. 
To help the perceptions of the animal, the many-jointed 
filament which strikes the water is fringed with hairs of 
great delicacy, standing out at right angles to the stalk, 
so that the slightest vibrations cannot fail to bo conveyed 
to the seusorium. This may be called the outer ear; but 
in the interior of the basal joint, which is large and swollen, 
there is a cochlea, or inner ear, having calcareous walls of 
* Ann. and Mag. of N. H., July 1S5 5, p. 40. 
