HOW CRABS HEAR AND SMELL 63 



On its head, as perhaps you know, a crab has 

 two pairs of feelers. We call them the " lesser 

 feelers" and the "greater feelers." Now if you 

 were to look at the first joint of the lesser 

 feelers through a good microscope, you would 

 find on each a little gland, or bag, contain- 

 ing a very tiny drop of salt and water. These 

 are the crab's ears. Of course they are not 

 nearly so good as our ears are. Indeed, I do 

 not think that a crab can hear sounds in the 

 air at all. But water carries sounds much 

 more readily than air does, so that if you were 

 to dive into a lake, or into the sea, on a calm, 

 still day you could easily hear the beat of the 

 oars in a boat half a mile away. And the ears 

 of the crab are made in such a way that they 

 can hear sounds in the water quite well, 

 even though they may be deaf to sounds in 

 the air. 



Then if you look at the first joint of the greater 

 feelers through the microscope, you will see two 

 other tiny glands. These are the crab's noses, 

 by which it can smell odours in the water just 

 as we can smell odours in the air. It always 

 seems to find its food by scent, and if one of 

 those basket-like traps which we call crab-pots 

 is baited with a few pieces of decaying fish and 

 lowered into the sea, crabs will smell the bait 

 from quite a long distance away, and come 

 hurrying up to obtain a share in the banquet. 



