CRABS, PRAWNS, AND LOBSTERS 1375 



Now taking the last-named animal as the repre- 

 sentative of his class, let us examine one of his inner 

 antennae first. It consists of a jointed stem and a ter- 

 minating bristle ; the latter furnished with small hairs 

 common to the general surface of the body, and 

 with long, delicate, membraneous filaments (seta), 

 often improperly called cilia, which are larger and 

 much more delicate in structure than the ordinary 

 hairs. 



The basal joint is greatly enlarged: if it be care- 

 fully removed from its connection with the head, and 

 broken open, it will be found to inclose in its cavity, 

 a still smaller chamber, with calcareous walls of a 

 much more delicate character than the outer walls. 

 This internal shell is considered by Mr. Spence Bate 

 to be a cochlea, from its analogy, both in structure 

 and supposed use, to the organ so named in the in- 

 ternal ear of man and other vertebrate animals. It 

 is situated, as has been said, in the cavity of the basal 

 joint of the internal antennae, and is attached to the 

 interior surface of its wall furthest from the median 

 line of the crab. It has a tendency to a spiral form, 

 but does not pass beyond the limits of a single con- 

 volution. 



If this interior cell does indeed represent the 

 cochlea of more highly constructed ears to which 

 it bears some resemblance, both in form and struc- 

 ture then it seems to identify, beyond dispute, these 

 inner or upper antennae as the organs of hearing. 



Now with this conclusion agrees well the man- 

 ner in which the living animal makes use of the 

 organs in question. The crab always carries them 



