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FIRST BOOK OF ZOOLOGY. 



which fringe the arms may be S2en. The jointed structure 

 of these appendages and their arrangement in pairs show 

 that the creature does not belong to the shell-fish or mol- 

 lusks, as its shell might seem to indicate. 



In past times many able naturalists classed these creat- 

 ures with the mollusks, because they judged from the ex- 

 ternal appearances of the shell, which was limy. A careful 

 study of their anatomy and development proved their rela- 

 tions to the crustaceans, and that they had no affinities what- 

 ever with the mollusks. In their growth they moult, in this 

 act shedding all the skin, and at certain times in the summer 

 the water will contain myriads of their cast-off skins. The 

 shell, however, is not shed. 



Fig. 141.— Earlt Stages op a Barnacle: A, shortly after leavingr the Egg; «?, Eyes: S, 

 having acq-iired a Bivalve Shell, and just before becoming attached, represented upside 

 down ; T, Appearance after becoming attached— Side-Vlew ; B, Top-View of still later Stage, 

 with the Shell forming .iround it ; E, Side- View of Later Stage, showing Appendages pro- 

 truded. (The little marks at the sides of the figures indicate the natural size of the object. 

 A, B, highly magnified ; all of these Views are m.agnified, and, with the exception of Z>, 

 are reduced from figures of C. Spence Bale.) 



