CiEiarEDiA.- 



-CRUSTACEA.- 



-Lepadhi.t:. 



293 



Btitutiiig the tail. TLe thoracic legs are six pairs in 

 number, in the female all terminated b}' a double claw, 

 serving both as organs of motion, prehension, and mas- 

 tication. The abdominal legs are also six pairs, folia- 

 ceous in structure, and serving the purpose of swim- 

 ming and respiration. The nervous system consists 

 of a principal medullary mass, which surrounds the 

 oesophagus like a ring, giving oil' nerves to the parts 

 belonging to the head and thorax ; and a large cord 

 which extends from this downwards along the median 

 line of the abdomen, sending off nerves to the abdominal 

 regions and the tail. 



LiMULUS, Krao-CRAB. — This is the 

 only genus belonging to the Xiphosura, 

 and the species are not numerous. Some, 

 however, are of large size, occasionally 

 attaining the length of two feet. They 

 are all marine, inhabiting the seas of 

 India, China, Japan, and the coasts of 

 North America. They seem to prefer 

 living on sandy shores; and in order to '< ''"■ 

 avoid tbe gieat heat of the sun, which 

 proves fatal to them, they bury them- 

 selves in the mud. The young undergo 

 considerable changes in their progress 

 to maturity; for at first they have no 

 tail, their abdominal buckler is rounded posteriorly, 

 and the sixtli pair of abdominal legs are undeveloped. 



The male is distinguished from the female by tbe 

 first and second pairs of thoracic feet being swollen, 

 and moreover destitute of the didactyle claw. The 

 long tail of one of the species from the Moluccas is 

 used by the natives as a point for their arrows, and the 

 wounds caused by them are said to be dangerous. In 

 America, where they are common, the large she'Is are 

 used by the inhabitants to lade water with, and the 

 animals themselves ai'e used to fatten pigs. In China 

 the eggs are used as food by the natives, and in Japan 

 a species is figured in their primitive zodiac as the 



raK. 



^m^^^^'^^'"^ 



Limnlus mfiluccanus. 



representative of the constellation Cancer. The species 

 licre represented (fig. 199) is Lhnulus mulucctiniis. 



Class — CIRPJPEDIA (Barnacles, or Sea-acorns). 



TuE Cirripeds are now universally admitted to be 

 Crustaceans, though till lately they used to be classed 

 with the Mollusca, on account of their shells. 



They are articulated animals, contained within a 

 hard covering composed of several pieces, and consist- 

 ing of laminie of calcified chitine. The body of the 

 animal is inclosed in a sac lined with a most delicate 

 membrane of chitine, which in one group is prolonged 

 into a peduncle and contains the ova. It is distinctly 

 articulated, and is placed with the back downwards. 

 The part which is called the abdomen has two rows of 

 fleshy lobes, each furnished with long horny appendages, 

 provided with many-jointed curled hairs or cirrhi to 

 the number of twelve pairs, which are constantly being 

 protruded and withdrawn again through an aperture in 

 the shell. They are the feet of the animal transformed 

 info these organs, and by means of them a current is 

 produced in the water, which attracts to the mouth the 

 objects which serve as food. The Cirripeds have man- 

 dibles and jaws very similar to other Crustacea, and 

 recent observations prove them to be possessed of eyes. 

 Their nervous system is ganglionic; they have a double 

 circulation of blood ; and the)' respire by means of 

 branchia? or gills, the form of which varies. The greater 

 part of them are hermajihrodite. Like the majorit}' of 

 the Enlomnstraca, to which they are closely allied, the 

 young undergo gieat changes in their progress to 

 maturity. When first liafclied from the egg they are 

 exceedingly small ; but when they have increased in 



size, they resemble the larv.-E of the Cyclops. They 

 float freely in the sea, swimming rapidly with their 

 back downwards. They soon become invested with a 

 coriaceous shell, and they now begin to look out for a 

 fit place to which they may attach themselves. Hav- 

 ing found this, they adhere to it by the part of the body 

 near the head, and in a few days afterwards they throw 

 olT their external covering. The shelly valves then 

 form, consisting at first exclusively of chitine ; the 

 antennae disappear, being cemented to the surface of 

 attachment ; the eyes remain, but in a more or less 

 rudimentary form ; three more pairs of legs are developed, 

 and then the animal assumes its perfect state. During 

 this time the Cirriped, like the other Crustacea, espe- 

 cially the Entomostraca, throws off its covering or 

 moults at frequent intervals, and is very rapid in its 

 growth. 



The greater part of the Cirripedia are arranged in 

 two large families — the Pedunculated Cirripeds, or 

 Lepadid^e ; and the Sessile Cirripeds, or Balaxid^e. 



I. LEPADIDiE [Pedunculated Cirripeds, or 

 Barnacles). 



The Lepadidce are characterized by having a length- 

 ened peduncle, which is coriaceous, hollow, flexible, 

 and provided with muscles, by means of which they 

 attach themselves to submarine bodies. The species 

 are tolerably numerous, and are found extending over 



