62 GENERAL ZOOLOGY 



around in the water until its first moult, when it acquires 

 more legs and the form characteristic for its particular 

 species. After the nauplius stage some kinds of crusta- 

 ceans become Copepoda, others Ostracoda, etc., but all 

 agree pretty closely up to the time when their nauplius 

 skin is shed. When the embryology of a barnacle came to 

 be studied it hatched from the egg as a nauplius! Since 

 this fact was discovered zoologists have not questioned the 

 right of barnacles to be known as relatives of Cyclops, 

 Daphnia, and other crustaceans. The life history of a 

 barnacle indicates that its race developed to a free swim- 

 ming stage comparable to the adult forms of other entomos- 

 tracans; then took up a sessile existence, specialized along 

 new lines, and even degenerated somewhat because it led 

 an inactive life. Fig. 32 shows larval and adult stages of 

 the barnacle and two of its relatives. 



