ISOPODA. 
431 
observations on the circulation of the Isopoda, and especially in the Ligife. The heart has 
the form of a long vessel, extended above the dorsal face of the intestine ; 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 
ganglion. 
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 by 
changing their skins. [M. Milne Edwards, in his interesting “ Observations sur les change- 
mens de forme que divers Crustaces eprouvent dans le jeune dgef (published in the Annates 
des Sciences Naturelles,) has given a detailed account of the peculiarities which distinguished 
the young individuals of Cymothoa trigonocephala and Anilocra mediterranean 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 branchiae in a state 
fitted for that function. 
This order, in the system of Linnaeus, consists of the genus 
Oniscus, — 
[ which we distribute into six sections. 
I The first section, Epicardes, Latr., is composed of parasitic Isopods having neither eyes nor antennae, 
of which the body is very flat, small, and oblong in the males, but much larger in the females, of an 
j oval form, narrow amd rather bent posteriorly, concave beneath, with a thoracic rim, divided on each 
side into five membranous lobes, the legs being inserted on this rim, very small and bent round, and 
1 fit neither for crawling nor swimming ; the under-side of the tail is furnished with five pairs of small 
; ciliated imbricated plates, answering to the same number of segments, and arranged into two longi- 
! tudinal rows, but the posterior extremity of the body is not furnished with appendages. The mouth 
i only distinctly exhibits two membranous plates, applied upon another of the same consistence, being 
i‘ 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, but their exceedingly minute size 
' seems to render the act of coupling impossible. These Crustacea form only a single subgenus, — 
1 Bopyrus, Latr., the common and typical species of which is the Bopyrus crangorum, Fab., which is parasitic 
upon the Common Prawns, Palcemon squilla and serratus, affixing' itself beneath the carapax, upon the branchiae, 
!i when it produces on the side of the body attacked a tumour or swelling like a lens. The fishermen of La Manche 
1 believe that these parasites are young soles, [to which fish they bear a slight resemblance in form]. 
’ M. Risso has described a second species [B. Palemonis, Risso, Crust. Nice. p. 148], beneath the body of the 
;| female of which he observed betw'een eight and nine hundred minute young ones, [easily visible with a lens, of a 
ij greyish white colour, and which the parent has always the instinct to deposit in the places frequented by the 
li Palaemons ; and as soon as the young are free they attach themselves to their prey]. 
I The second section, Cymothoada, Latr., comprises those Isopoda which have four distinct antennae, 
Ij setaceous, and ordinarily terminated by a multiarticulate filament, having eyes and a mouth composed 
li of the ordinary parts (see the general observations upon the Malacostraca Edriopthalma), and vesicular 
ji branchiae disposed longitudinally in pairs. The tail is composed of four or six segments, with a swim- 
i ming plate on each side near the tip, and the five legs are generally terminated by a strong hook or 
claw. All the Cymothoada are parasites. 
In Serolis, Leach, the eyes are placed upon tubercles on the back of the head, and the tail is composed of only 
four segments. The antennae are arranged in two lines, and terminated by a multiarticulate filament. Beneath 
j the three basal segments of the tail, between the ordinary appendages, there are three others, transverse, and 
1 terminated posteriorly in a point. One species was only known [to Latreille, namely, the Cymothoa paradoxa, Fab. 
