22 THE LIFE OF CRUSTACEA 



Lobster, enclosed in a hard shelly covering, the sense 

 of touch must be very dull, if not altogether absent. 

 This, however, is not the case. What is probably a 

 very delicate tactile sense is provided for by the 

 numerous hairs which are found, of many sorts and 

 sizes, all over the body and limbs. Each of these 

 hairs is really a hollow outgrowth of the chitinous 

 covering, containing a delicate prolongation of the 

 soft tissues underneath, and also supplied, in many 

 if not in all cases, with a nerve-fibre, so that the 

 slightest movement of the hair caused by contact 

 with a solid body is perceived by the animal. Many 

 of these hairs are themselves beset with delicate 

 secondary hairs, arranged so that the whole looks 

 like a feather or like a bottle-brush. These hairs 

 are adapted for detecting slight movements or vibra- 

 tions in the surrounding water. 



Whether Crustacea living in water can hear, in 

 the sense in which the word is used of animals 

 living in air, is doubtful ; but it is certain that they 

 are extremely sensitive to vibrations only a little 

 coarser, so to speak, than those we know as sound. 

 The Lobster, and many other Crustacea, do indeed 

 possess a structure which was long supposed to be 

 an organ of hearing, and may possibly in part fulfil 

 that function, although it is now known that that is 

 not its only or even its chief use. It consists of a 

 small cavity in the basal segment of the stalk of the 

 antennule, opening to the outside by a narrow slit 



