444 



CRUSTACEA. 



the posterior pair becomes the rudiment of the anterior jaws 

 (mandibles) of the oral cone, which is still closed and on which the 

 first rudiments of the maxillee and under lip are already visible. 

 The oral cone is followed by the thoracic region with six pairs of 

 birarnous Copepod-like swimming feet, and a minute three-jointed 

 abdomen, which terminates in two caudal appendages and caudal seta?. 

 The pupa has a large pair of compound eyes at the sides of the un- 

 paired eye-spot, and swims about by means of its swimming feet. It 

 appears not to take in food. The material necessary for its further 

 changes is stored up principally in the cephalic and dorsal regions in 

 the form of a largely-developed fat body. 



After swimming about for a longer or 

 shorter time, the pupa fixes itself by 

 the suctorial disc of its bent antennae 

 to some foreign body. The parts of the 

 adult Cirripede are now visible beneath 

 the skin, and the cement gland begins to 

 secrete a cement, which hardens and so 

 brings about the permanent attachment 

 of the young animal. In the Lepadidce 

 the region of the head above and be- 

 tween the antenna? grows so much that 

 it projects from the pupal integument, 

 beneath which the calcareous pieces of 

 the shell of the Cirripede can be seen, 

 and after the moulting of the chitiiious 

 skin of the pupa constitutes the fleshy 

 peduncle by which the animal is attached, 

 and into which the rudiments of the ova- 

 ries project (fig. 353). The paired eyes of 

 the free-swimming Cypris larva disappear, 

 while the unpaired pigment spot remains. 

 The mouth parts become fully differen- 

 tiated, and the biramous swimming feet become short, many-jointed 

 cirriform appendages. 



The Cirripedia are marine animals. The}' attach themselves to 

 various foreign objects. They are found fixed, usually in groups, to 

 logs of wood, rocks, mussel shells, Crustacea, the skin of whales, etc. 

 Some, as Litholrya, Alcippe, and the Cryptopialidce, are able to bore, 

 into Lamniellibranch shells and Corals, while the Rhizocephala are 

 parasitic on Crustacea. In the Rhizocephala the body is saccular, 



Fi<;. 353. Young Lepas after 

 disappearance of the two horny 

 valves of the shell and the 

 straightening of the anterior 

 part of the head (stalk) , which 

 in the pupa stage is bent. 



