36 A NATURAL HISTORY OF THE SEAS 



by the bather. On a very still day one may hear a gently 

 hissing sound which is caused by countless millions of 

 these creatures oscillating the jointed lids of their residences 

 in impatient anticipation of the returning tide. In the 

 far north these barnacles reach a large size, one species 

 having a shell fully four inches in height. 



Another abundant form is the Goose Barnacle (Lepas 

 anatifera), which may be recognised by its flattened shell 

 and the long tough sinuous stem which anchors it to floating 

 timber and which represents the last remnants of the 

 creature's head. In mediaeval times this crustacean was 

 in some way confused with the barnacle goose, the bird 

 having been seen in the vicinity of the tree branches 

 which at low tide revealed themselves as being covered 

 with barnacles. It thus happens that many quaint old 

 woodcuts testify to the once general belief that the barnacles 

 grew on trees and actually developed into birds. Some 

 assert that the belief, which dates from the twelfth century, 

 had its origin in a priestly desire to give the goose a vege- 

 table origin and so extend the Lenten bill of fare. 



On our southern coasts and much more abundantly in 

 the Mediterranean there abounds a form, allied to the 

 common Goose Barnacle, but having less solidly formed 

 shells, which is sold for food. 



One species of sessile barnacle, Tubicinella, actually 

 burrows into the skin of whales. 



A very remarkable group of barnacles has carried de- 

 generation yet a stage farther. The seaside visitor may 

 often find a crab with a tough fleshy knob firmly attached 

 to its abdomen. This is the Sack Barnacle, Sacculina. 

 It hatches from an egg into a free-swimming larva almost 



