ARTHROPODA. 239 



appearance, although they are alike in fundamental 

 structure. The largest of the Crustacea is the giant crab 

 of Japan whose spider-like legs are said to reach 18 or 20 

 feet from tip to tip. 



256. Barnacles. The barnacles are attached in their 

 adult stage, although they are free-swimming in the 

 embryo. They develop strong, limy plates which suggest 



FIG. 84. Violet land crab. Adult. After Shufeldt. 



Questions on the Figure. Compare this with all the figures of 

 crabs available, and note the points at "which the chief variations 

 occur. Compare crabs and lobsters with respect to body regions, 

 segmentation, and appendages. 



the shell of the mollusk, and for this reason they were 

 long classed as such. Their manner of development and 

 the structure of the appendages show, however, that they 

 are degenerate Crustacea. They attach themselves to the 

 rocks and piles from a point above low tide to considerable 

 depths. Floating objects are sure to become covered 

 with them. The hulls of ships may become foul with 

 them during long voyages. 





