CRABS AND SHRIMPS. 178 



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. Spenee Bate (to 

 whose excellent memoir * I am indebted for these expla- 

 natory details) that the inner antennas are real ears. 



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

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

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

 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 antennas. 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 sepa- 

 rate 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 eentral line of the 

 animal are fixed two small hinges. When the operculum 



* " Annals of Nat. Hist." for July, 1855. 



