200 EVENINGS AT THE MICROSCOPE 



Now taking the last-named animal as the representative 

 of his class, let us examine one of his inner antennae first. 

 It consists of a jointed stem and a terminating bristle; the 

 latter furnished with small hairs common to the general 

 surface of the body, and with long, delicate, membranous 

 filaments (setce), often improperly called cilia, which are 

 larger, and much more delicate in structure than the ordi- 

 nary hairs. 



The basal joint is greatly enlarged: if it be carefully 

 removed from its connection with the head, and broken 

 open, it will be found to enclose in its cavity a still smaller 

 chamber, with calcareous walls of a much more delicate 

 character than the outer walls. This internal shell is con- 

 sidered by Mr. Spence Bate to be a cochlea, from its 

 analogy, both in structure and supposed use, to the organ 

 so named in the internal ear of man 

 and other vertebrate animals. It is 

 situated, as has been said, in the 

 cavity of the basal joint of the in- 

 ternal antenna, and is attached to 

 the interior surface of its wall fur- 

 KAR OF CRAB, FROM BEHIND, fl^st f rom the median line of the 

 Crab. It has a tendency to a spiral form, but does not 

 pass beyond the limits of a single convolution. 



If this interior cell does indeed represent the cochlea 

 of more highly-constructed ears to which it bears some 

 resemblance, both in form and structure then it seems to 

 identify , beyond dispute, these inner or upper antennae as 

 the organs of hearing. 



Now with this conclusion agrees well the manner in 

 which the living animal makes use of the organs in ques- 

 tion. The Crab always carries them erect and elevated; 



