ARTHROPODA. 187 



objects from their transparency : mounted specimens 

 may be obtained from dealers in such things, and the 

 student may find numerous forms for himself. Some 

 undergo metamorphosis, the early larva being of the 

 form called a Naupliits, having first been described 

 under that name. Gypris is a genus whose fossil 

 shells are found in many geological deposits. The 

 Carp-lice are parasitic forms of Entomostraca. 



The Glrripedia, or Barnacles, are an especially 

 interesting order. These develop from a Nauplius 

 larva (Fig. 49), and change into a higher form 

 which is like a Oypris ; it has antennae, an unpaired 

 eyespot and a pair of compound eyes beside, and 

 a gland called a cement gland, at the head end. 

 This larva fixes itself by the antennae, being glued 

 down by the secretion of the cemeut gland, loses 

 its paired eyes, and lives for the remainder of its 

 days standing on its head. Prof. Huxley says, it is 

 "a, Crustacean fixed by its head, and kicking the 

 food into its mouth with its legs." The Long-necked 

 Barnacles (Lepas anatifera, fig. 51, frontispiece) ai-e 

 common on wreckage ; they have a coloured shell, 

 china blue with a streak of orange at the edge of the, 

 valves, in texture like that of a mollusc, but composed 

 of several plates, bilaterally arranged. From the 

 appearance of this shell, the barnacles were formerly 

 supposed to be molluscs. The "stalk" is a tough 

 leathery structure, containing the cement gland and 

 its duct, and in the adult the ovaries; it is flexible, 

 and bends about with a slow movement and with 



