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 stont joints, at the tip of which are 

 three threads, of which two are of great length, and formed 

 of numberless rings, and the third is short. These organs, 

 then, constitute the inner pair of antennce. 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 antennce. The former are 

 the organs of hearing, the latter those of smelling. 



In the living animal, the inner antennae 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 tenants 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, standiog out at right angles to the stalk, 

 so that the slightest vibrations cannot fail to be conveyed 

 to the sensorium. This may be called the outer ear; but 

 in the interior of the basal joint, which is large and swollen, 

 ther3 is a cochlea, or inner ear, having calcareous walls of 



* Ann. and Mag. of N. H., July 1855, p. 40. 



