BARNACLES 



345 



in a fold of skin, usually with calcareous plates. The anterior 

 antennae are involved in the attachment ; the posterior pair 

 are rudimentary. The oral appendages are small, and in part 

 atrophied. In most there are six (or less frequently four) 

 pairs of two-branched thoracic feet, which sweep food particles 

 into the depressed mouth. The abdomen is rudimentary. 

 There is no heart. The sexes are usually combined, but 

 dimorphic unisexual forms also occur. The hermaphrodite 

 individuals occasionally carry pigmy or " complemental " 

 males. The spermatozoa are mobile, which is unusual 

 among Crustacea. 



Lepas, the ship-barnacle, is as an adult attached to floating logs and 

 ship-bottoms. The anterior end by which the animal fixes itself is 

 drawn out into a long flexible stalk, containing a cement gland, the 

 ovaries, etc., and involving in its formation the first pair of antennae and 

 the front lobe of the head. The second antennae are lost in larval Hfe. 

 The mouth region bears a pair of small mandibles and two pairs of 

 small maxillae — the last pair united into a lower lip. The thorax has 

 six pairs of two-branched appendages, and from the end of the rudi- 

 mentary abdomen a long penis projects. At the base of this lies the 

 anus. Around the body there is a fold of skin, and from this arise five 

 calcareous plates, an unpaired dorsal carina, two scuta right and left 

 anteriorly, two terga at the free posterior end. The nervous system 

 consists of a brain, an oesophageal ring, and a ventral chain of five or 

 more ganglia. There is a vestige of the nauplius eye. No special 

 circulatory or respiratory organs are known. Two excretory tubes 

 lead from (coelomic) cavities to the base of the second maxilla?, and are 

 probably comparable with shell glands and with nephridia. There is a 

 complete food canal and a large digestive gland. Beside the latter lie 

 the branched testes, whose vasa deferentia unite in an ejaculatory duct 

 in the penis. From the much-branched ovaries in the stalk, the ovi- 

 ducts pass to the first thoracic legs, where they open into a cement - 

 making sac, opening to the exterior. The eggs are found in flat cakes 

 between the external fold of skin and the body. 



The life-history. Nauplius larvae escape from the egg-cases, and, 

 after moulting several times, become like little Cyprids. The first 

 pair of appendages become suctorial, and, after a period of free- 

 swimming, the young barnacle settles down on some floating object, 

 mooring itself by means of the antennary suckers, and becoming firmly 

 glued by the secretion of the cement glands. During the setthng and 

 the associated metamorphosis, the young barnacle fasts, living on a 

 store of fat previously accumulated. Many important changes occur, 

 the valved shell is developed, and the adult form is gradually assumed. 



The food consists of small animals, which are swept to the mouth by 

 the waving of the curled legs. Growth is somewhat rapid, but the 

 usual ecdysis is much restricted, except in one genus. Neither the 

 valves, nor the uniting membranes, nor the envelope of the stalk, are 

 moulted, though disintegrated portions may be removed in flakes and 

 renewed by fresh formations. In the allied genu* Scalpellum, some 

 are like Lepas, hermaphrodites, without complementary males {So. 



