CRABS AND SHRIMPS 201 



and is incessantly striking the water with them, with a 

 very peculiar jerking action, now and then vibrating, and, 

 as it has been called, "twiddling" them. These antennae, 

 therefore, appear to be always on the watch: let the ani- 

 mal be at rest, let it be feeding, no matter, the superior 

 antennae are ever elevated and on constant guard. 



The lengthened and delicate setae with which they are 

 furnished are, moreover, peculiarly adapted to receive and 

 convey the most minute vibratory sensations from the me- 

 dium 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 explana- 

 tory details) that the inner antennae are real ears. 



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

 deavor 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 or- 

 gan. Our friend Mr. Bate must assist us again. He will 

 tell us to look at the outer or lower antennae. 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, with 

 difficulty distinguishable into their constituent articula- 

 tions; while in some species their position can be indi- 

 cated only by the presence of the olfactory operculum. 



This important little organ varies in its construction in 



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



