ORGANS OF SOUND— MOLLUSCA— CRUSTACEA. 61 



whether they are affected by a real noise, or whether 

 they are merely conscious of a concussion or yibration. 



As regards the lower animals, it appears to me, I con- 

 fess, tliat many organs have been described as auditory, 

 on grounds which are anything but satisfactory. At 

 the same time, it cannot be doubted that many of the 

 lower animals do possess the power of hearing, especially 

 as some have elaborate organs for the production of 

 sound. 



Among the lowest groups, none of the Protozoa or 

 Coelenterata are known to produce sounds, and in the 

 Mollusca, also, the power is very rare. The Pectens, 

 which are the most lively of bivalves, moving actively 

 by the sudden opening and closing of their valves — as 

 Pliny says, " Saliunt Pectines et extra volitant seque 

 ipsi carinant " — also produce in the same way a certain 

 sound, which Aristotle * gives as an exceptional case 

 among the Mollusca. 



Nor is the production of sound much more frequent 

 among the Crustacea. In one genus of crabs (Ocypoda), 

 the claw bears a rasp, or file, which can be rubbed against 

 a ridge on the basal segment of the limb, and thus 

 produces a harsh, jarring sound. Some of the lobsters 

 also (Palinurus) make a noise by rubbing one segment 

 of the antennae against another ; but, considering that 

 the ear is well developed in this group, it is rather 

 remarkable how few of them are known to possess the 

 power of producing sounds. 



Passing on to the insects, the song of the Cicada has 

 been celebrated from time immemorial ; the chirping of 

 the crickets and grasshoppers is also familiar to us all. 



For the reasons, however, already alluded to in the 

 * " Historia Animalium." 



