CRABS AND SHRIMPS. 173 



let the animal be at rest, let it be feeding, no matter, the 

 inner antennae are ever elevated, and on constant guard. 



The lengthened and delicate seta? with which they are 

 furnished are, moreover, peculiarly adapted to receive and 

 convey the most minute vibratory sensations from the 

 medium in which they are suspended ; and, on the whole, 

 it seems to be satisfactorily settled by Mr. Spence Bate 

 (to whose excellent memoir* I am indebted for these 

 explanatory details) that the inner antennae are real ears. 



Having thus taken our Crab by the ears, we will en- 

 deavour next to tweak his nose. But stay, we must 

 lind it first. We turn our horny gentleman up, and in 

 his Hat ancient face we certainly discern little sign of a 

 nasal organ. Our friend Mr. Bate must assist us again. 

 He will tell us to look at the outer or lower antenna-. 

 We will look, accordingly, magnifier in hand, while he 

 makes it clear to us that these are a pair of noses. 



Each of these organs is formed of a stem, consisting 

 in general of five joints and a filament of many minute 

 joints. In the Prawn and the Lobster all the five joints 

 of the stem are distinct; but in the Crab the whole are, as 

 it were, soldered together into a compact mass, so that the 

 separate articulations are scarcely to be distinguished ; 

 while in some species their position can be indicated only 

 by the presence of the olfactory operculum or lid. 



This important little organ varies in its construction in 

 the different families of Crustacea. In the Crab it is a 

 small movable appendage, situated at the point of junction 

 between the second and third joints ; it is attached to a 

 long calcareous lever-like tendon, at the extreme limit of 

 which is placed a set of muscles, by which it is opened 

 and closed ; to assist in which operation, at the angle of 

 the operculum most distant from the central line of the 

 animal are fixed two small hinges. When the operculum 



* u 



Annals of Xat. Hist." for July, 1S55. 



