BARNACLES 



251 



Balanus. A, external view 

 scutum ; t, tergum. 



mouth of the animal, which is dependent upon such food as comes 

 within range of its tentacles. 



Their life-history is interesting. The young barnacle, called a 

 nauplius, in no way resembles the adult. When it emerges from 

 the egg it is a free and independent animal, with one eye, three 

 pairs of legs, and a single shell. It 

 swims about for a while and moults 

 several times. It then has two eyes, two 

 shells, and six pairs of legs. At this 

 period it seeks a permanent home, and 

 attaches its anterior end to the object it 

 selects by means of its antenna?, which 

 have become suckers. It makes its hold 

 secure by secreting a cement which 

 permanently fastens it to the spot. It 

 then undergoes metamorphosis, loses its bivalve shell and its 

 eyes, and attains its characteristic cirripeds, or curled feathery 

 legs, and a new shell covering. During these transformations, 

 from the time it be- 

 comes fixed until it at- 

 tains its adult form, 

 the barnacle fasts, liv- 

 ing by the absorption 

 of its own animal fat. 

 Its food subsequently 

 consists of the minute 

 animal forms which 

 abound in the sea. Its 

 further growth is by 

 moulting, but parts 

 only of its covering 

 are disengaged ; the 



B 



sk 



~QX> 



l-:,i i, i a us. B, anatomy: a, antennules: ail. adductor muscle ; m, 

 muscles of scuta and terga; o, edge of parapet; ov, ovary ; ovi, ovi- 

 duct ; ac, scutum ; sk, parapet ; t, tergum ; too, female aperture. 



shellis permanent, and 

 its successive stages 

 of growth are marked 

 upon it by lines, as in mollusks. The lining of the shell, or en- 

 veloping skin of the animal, and also the cuticle of the legs are 



