198 EVENLNGS AT THE MICROSCOPE. 



great Eatable Crab each pair is very small, and they 

 are dissimilar. 



Now taking tlie 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 

 terminating bristle ; the latter furnished with small 

 hairs common to the general surface of the bodj, 

 and with long, delicate, membranous filaments {seice), 

 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 connexion 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 that the outer walls. Tliis in- 

 ternal shell is considered by Mr. Spence Bate to be a 

 cochlea, from its analogy, both in structure and sup- 

 posed 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 internal antenna, and is attached to the interior 

 surface of its wall farthest 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 convolu- 

 tion. 



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 upjier 

 antennae as the organs of hearing. 



Now Avith this conclusion agrees well the maimer 

 In which the living animal makes use of the organs in 



