THE ANIMAL LIFE OF THE GROUP. ' 473 



it will immediately seek shelter in the nearest shell at hand. The crab will 

 back into its new home, inserting its tender abdomen into the shell until the 

 aperture is plugged by its claws and the hard part of its body. 



Often at low tide during the day a dozen or more of these active creatures 

 will be found carefully hidden away under some loose stone on the reef. 

 When disturbed they start off in all directions, each sheltered in a different 

 species of shell and each carrying its own borrowed house on its back like a 

 snail. Not infrequently other animals, as barnacles, oysters and sea-anemonies 

 take up their permanent residence on the shell occupied by a hermit crab and 

 are in this way carried about by them. 



Barnacles. 



There is little in the appearance of adult barnacles to suggest that they 

 are in any way related to their crab and lobster cousins. Such is the case, 

 nevertheless, and by zoologists they are looked upon as furnishing an excellent 

 example of degeneration through quiescence, for when they hatch from the 

 egg they are free swimming animals that closely resemble the young ^'^ form 

 of the crabs and shrimps, with but a single eye. Later on they have six pairs 

 of swinnning feet, a pair of compound eyes, and two well-developed antennte, 

 and are still free swimming animals. But when the creature makes the final 

 change to the adult condition, it attaches itself by means of a cement-like sub- 

 stance to a stone, shell, pile or floating log, or to the bottom of a ship, and 

 gives up all attempts at locomotion. It then loses its compound eyes and its 

 feelers, and develops a protecting shell. The swimming feet become modified 

 into grasping organs and henceforth it abandons any attempt to look and act 

 like other Crustacea and devotes its energies to fanning such food as comes its 

 way into its mouth, with its legs. There are two main groups of the order, n 

 including the barnacles, that are liable to attract attention on the sea-shore. 

 One family ^^' includes the stalked species familiarly known as goose mussels or 

 goose barnacles, a name derived from an ancient belief that if one fell from its 

 support it turned into a goose. They iisually occur hanging by the long stalk i" 

 to the bottoms of ships, to floating timber or submerged wood of any kind. 

 The sessile barnacles,^' acorn shells, or pioeoe as they are called by the natives, 

 are everywhere abundant along the shore. The entire animal is enclosed in a 

 tent-shaped shell composed originally of six pieces, which is capped by an 

 operculum made up of foiu" valves. 



Unfortunately, the shore forms have not as yet been fully studied. A 

 dozen species of barnacles were eniunerated by my friend. Dr. Pilsbry, from 

 the material gathered by the ship Albatross. But one of these, a species of 

 acorn barnacle i* belonging to the typical genus of that family, was secured in 

 shallow water. The remainder were deep-water or off-shore forms, mo.st of 

 them occurring in water two or three hundred fathoms deep. Of the twelve 

 species secured, eight proved to be undescribed. A careful study of the shore 



