264 TEE SEA SHORE 



portion of the body. Then, with a much more rapid movement, 

 the appendages will be withdrawn, and the shell closed. These 



alternate movements are con- 

 tinued incessantly, and are the 

 means by which the animals 

 provide themselves with both 

 food and air. The reader should 

 also obtain some specimens of 

 the larger species for the exami- 

 nation of the shell, the structure 

 of which is interesting and, of 

 course, peculiar to this order. 



In general structure and 

 habits Barnacles are very similar 

 FIG. 195. THE ACOKK BABNACLB to the acorn barnacles, except 

 (Balanus porcatus) WITH Ap- that the bod is supp orted on a 



PENDAGES PBOTRUDED , , . , , 



tough stalk, which, as we have 

 already stated, is the modified 



anterior portion of the animal. These animals also may be easily 

 kept alive and examined in the indoor aquarium. They are not 

 creatures of the sea shore, but may often be obtained on masses of 

 timber that have been washed ashore, or from the bottoms of ships 

 that have been placed in the dry dock for repairs. 



Another order of the crustaceans the Copepoda, or oar-footed 

 group is so called on account of the bristled feet that are em- 

 ployed after the manner of oars when the creatures are swimming. 



These Copepods are small animals, so small indeed that the 

 compound microscope is generally necessary merely for the ex- 

 amination of their external characters. Many species inhabit fresh 

 water, and the study of the group is more commonly pursued by 

 the investigator of fresh-water pond life than by the sea-side 

 naturalist. However, marine species are abundant, and may be 

 captured in the open water or in rock pools by means of a muslin 

 net. As with the last order, some degenerate from the comparatively 

 complicated free-swimming and eyed larval state to blind and 

 limbless parasites that feed on the bodies of fishes and are known 

 as fish lice. 



The body of the typical copepod is distinctly segmented, and 

 the head and thorax are both enclosed in a hardened buckler. It 

 has two pairs of antennae, two pairs of foot jaws by which it captures 

 its prey, and four or five pairs of bristled feet for swimming. The 



