TSOPODA. 



431 



observations on the circulation of the Isopoda, and especially in the Ligiac. Ihe heart has 

 the form of a long vessel, extended above the dorsal face of the intestine j from its anterior 

 extremity are emitted three arteries, as in the Decapods, but from their examination it would 

 seem that the venous system is not so complete as in the Macroura. In respect to the 

 nervous system, there are nine ganglions, not including the brain, but the two anterior and 

 the two posterior are so nearly together that they may be reduced to seven. The second and 

 six following send forth nerves to the legs, and the tail is furnished with nerves from the last 



The females carry their eggs underneath the breast, either defended by scales, or in a pouch 

 or membranous sac, which they open in order to allow the young ones to escape ; these are 

 born with the form and parts peculiar to their own species, and merely increase in size bj 

 changing their skins. [M. Milne Edwards, in his interesting " Observations snr Irs change- 

 mciis de forme que divers Crustaces eprouvent dans le jeune age," (published in the Annates 

 des Sciences Naturelles,) has given a detailed account of the peculiarities which distinguished 

 the young individuals of Cymothoa trigonocephaly and Anilocra mediterranea, which had been 

 extracted from between the pectoral plates of the females. In the newly-hatched young, the 

 tail is longer and narrower than in the perfect animal, and it has only six thoracic segments 

 and six pair of legs.] 



The greatest number of the species reside in water. Those which are terrestrial have like- 

 wise need, as is the case with other Crustacea living out of the water, of a certain degree of 

 atmospheric humidity, in order to enable them to respire, and keep their branchial in a state 

 litted for that function. 



This order, in the system of Linnaeus, consists of the genus 



Oniscus, — 

 which we distribute into six sections. 



The first section, Epicabdes, Latr., is composed of parasitic Isopods having neither eyes nor antenna;, 

 of which the body is very flat, small, and ohlong in the males, hut much larger in the females, of an 

 oval form, narrow and rather hent posteriorly, concave heneath, with a thoracic rim, divided on each 

 Bide into five membranous Lobes, the legs heing inserted on this rim, very small and bent round, and 

 fit neither for crawling nor swimming ; the under-side of the tail is furnished with live pairs of small 

 ciliated imhricated plates, answering to the same numher of segments, and arranged into two longi- 

 tudinal rows, hut the posterior extremity of the body is not furnished with appendages. The month 

 only distinctly exhibits two membranous plates, applied upon another of the same consistence, being 

 of a quadrilateral form. The hollowed part of the body is filled with eggs, and near the situation 

 where they are discharged the presumed males are constantly found, hut their exceedingly minute 

 seems to render the act of coupling impossible. These Crustacea form only a single subgenus, — 



Bopynu, Latr., the common and typical species of which is the Bopyru* erangorttm, Pab., which Is parasitic 

 upon the Common Prawns, PaUemon iquilla and terrdtut, affixing itself beneath the carapax, upon Ihe brant 

 when it prodncea on the side of (he body attacked a tumonr or swelling like i lens. The fishermen of La Manche 

 believe that these parasites are young soles, [to which fish they bear ■ slight resemblance in fern . 



M. Risso has described a second species [/>'. Palemonit, EUsso, Crutt. Nice, p. 148], beneath the body of the 

 female of which he ohserTod hot ween eight and nine hundred minute young curs, [easily risible with a lens, of a 

 greyish white colour, and which the parent has always the Instinct to deposit in the places frequented i>> the 



Pals mow , and U SOOn as the VOIing are free the\ attach themselves to their prey]. 



The second section, Ctmotboasa, l.atr., comprises tl Isopoda which have four distinct ant 



setaceous, and ordinarily terminated by a multiarticulate filament, having eyes and a month com] 1 



of the ordinary part- | -ee the general observations upon the Mahicostiaca Kdriopthalma), and vesicular 



branchiae disposed longitudinally in pairs. The tail is composed of four or six segments, with a swim< 

 mini: pl.t' ach side near the tip, and the five legs are generally terminated by a strong hook or 



claw. All the Cj/mothoada are parasites. 



In 8erol Leach, 1 lari placedupon tubercles on the back of the head, and the tail is composed of only 



lenta. Theanl arranged In two lines, and terminated by a multiarticulate filament Beneath 



the three basal segments of the tafi, between the ordinary appendages, there are three others, transverse, and 



tei m mated posteriorly in a pout. m Only known to Uitrcillo, inrtnelv , the CyMnthmi /iiirtiiloi i, F.ih. 



