106 "MANY ISLES AND STRANGE PLACES" 



The reefs have sounds as well as sights of their 

 own, mysterious cracks and pops that seem to come 

 from nowhere. They are caused by little shrimps of 

 the genus Alpheus, which live hidden, usually in pairs, 

 among the sponge and coral. These Alphei are re- 

 markable for the gigantic size of one of their large 

 nippers, on one of the blades of which there is a big 

 tooth which, when the nippers are closed, fits tightly 

 into a hole in the other blade. The sound is said to 

 be made either by the sudden opening of the blades 

 and forcible extraction of the tooth from the socket, 

 like a cork from a pop-gun, or by the sudden closing 

 of the blades and sudden forcing of the tooth into 

 the socket, like a wad into a gun-barrel. Another 

 crustacean that makes a sharp clicking sound is 

 Gonodactylus chiragra, one of the locust-shrimps. It 

 has, instead of nippers, large ''raptorial feet," in 

 which the terminal claw folds down, like the blade of 

 a penknife, into a groove cut in the whole length of 

 the joint behind it. At the near end of the latter 

 joint, at a point corresponding with the tip of the 

 closed blade of the penknife, is an erectile spine, and 

 the noise which this animal makes seems to be pro- 

 duced by causing the blade of the knife (terminal 

 claw) to fly open, and to strike the erected spine as 

 it does so. The large rock - lobster (Palinurus 

 striahis), which one finds in these lagoons, is able 

 to make a weird, creaking noise by rubbing a 



