64 CRUSTACEA. 



text-books. To the lowest order, Cirripedia, belong 

 the barnacles (Figs. 36, 37,* 38-f) which whiten our 

 rocky shores, and the piles of our wharves and bridges 

 between tide-marks, with their innumerable shells. 

 Though formerly classed with the Mollusca, these ani- 

 mals are true Crustacea. Attention is called to them 

 here because they are familiar, and also because they 

 are good illustrations of what is known as retrograde 

 development. The young barnacles are free-swimming 

 (Fig. 36, a), but after a time they cement their forward 

 ends to the rocks by a sticky secretion which flows from 

 the antennae. The outer skin becomes calcified, and 

 forms a conical shell of several pieces (Figs. 37, 38, v). 

 In the top of the shell there are two valves, which, in 

 the living animal, open and close. When open, six 

 pairs of many-jointed appendages (Fig. 37, e \-e b) are 

 thrust out. These are beset with hairs, and, sweeping 

 through the water, they catch the food upon which 

 these creatures feed, and carry it to the mouth. Groups 

 of living barnacles may be obtained from the bottoms 

 of vessels, or from piles or rocks, and when placed in 

 sufficiently shallow water may be seen to use their legs 

 in feeding. The articulated or crustacean character 

 of these appendages can be readily seen in all but the 

 smallest species. 



As Huxley says, the barnacle is an animal turned 

 upside down, and kicking the food into its mouth with 

 its legs. To us, however, it is an important illustration 

 of the way in which a Crustacean may become adapted 

 to lead a sedentary life, and to get its food by fishing 



* Balanus tintinnabulum. t lialanus llameri. 



