. :: RAJ ! v 



CRUSTACEA. 



Te 







to aid OM i 



*; a cavity far ab 

 that barrow. UM la* 

 MM) to UM i 



iMMrtof portion at the thoracic extremities, 

 MM gMMral farm which w. bar. assigned it, 

 to HTT* for walking M well u swimming, or 

 it fur burrowing with facility, and 

 the mud. Thai io the Decapod* 

 of 'th Una* assumes a UnceoUtod 

 sagmsnt, especially 

 (Mal'nta, for example), appear* entirely 



Any no* who will tak* the trouble of going over this exrrllrnt 

 JMMhillilli with a oommon crab and lobster before him, will hare a 

 dear idea of UM locomotive system in these animals. 



We haw only further to add, that in a great number of specie* one 

 or eeraral pair* of UM thoracic extremhie* are modified *o a* to 

 beoooM iMtranMote of prehension ; aometime* it is the lost segment 

 at UM limb which, acquiring more than umial mobility, bends in such 

 a saar a* to form a hook with the preceding segment ; sometimes 

 it this |-niiil1tmfi*- sajinsnt which extends below or by the side of 

 UM last, so as to form a kind of immoreable finger with which it is 

 placed in opposition. In the first instance these instruments are 

 ifeaooiiaated subohelifunu claws, in the second cbel.-c simply, or 

 cadifonu daws. 



rUw (cbtliforni) of TMfkutt jferia/i/u. 

 ; , bind (maotu) sad immoreablc fln gtr ; e, crpu, or wrUt. 



Potrior foot of nrlplttaa JIuriatiliM. 



m, Hiuea (haacke) ; , trochsntrr ; r, thigh (femur) ; d, leg ; r, mcUtar- 

 sw;/, tanw, or asiL 



W* come now to the organs of digestion. The cheliform or sub- 

 ifcslifm m daw* may be considered as ancillary to this important part 

 of UM organisation of the Crustacea ; and there are other parts, the 

 detail* of which w* proceed to give before we enter at Urge into this 

 part of the subject. 



I 



1 



____ 



jsw^ot ; A, lu iatmal V.**, or U*.; .,,<, i 

 B, lu iW..l ta4>. , p.ip ;' . j^T of tb, 



p.lp. . J.W* tb. UM ,.,r .lib II. p.lp 4. U.rf ta 

 Ptr ; . ).. rf tw tm pat, , , diW. ,. ,,1 ^f, . J 

 (laafw) of lower Up. 



. . 



in UM MasHoaHnt Cnntanaiaa, raaoh in them their highest 



Mat; whilst in UM Hacking Crasteo.ua, which 



adapted for sticking, and in the interior of which are two slender 

 pointed proem 81 that act as lanoeU for the purpose of perforation, 

 m lieu of the true mandibles. 



The basilar articulations of the anterior thoracic extremities in 

 many species are employed to seize, hold fast, and in a . 

 decree comminute, the food ; and the most perfect developm 

 this design is manifested in the cheliform dawn of the lobsters and 

 crabs, with all their admirable modifications for powerful prehen 



The mouth is a mere opening of the short oaHophagus : nor is it 

 furnUhed with a tongue the organ so named (langue and languette) 

 is no more than a horny and lamellar process, performing in a degree 

 the functions of a lower lip. The oesophagus, which terminate* 

 without any interruption in the stomach, and Imtli parts, with one 

 striking exception in the case of the latter, which we shall presently 

 mention, present nothing remarkable, consisting, as well n the whole 

 of the intestinal canal, of two membranous layers, and presenting a 

 considerable resemblance to the same part of the organisation of the 

 higher animals. The stomach is globular and capacious, occupying 

 much of the area of the cephalic cavity, and consisting of two . ! 

 portions: 1, the cardiac region, surmounting the mouth and oeeo- 

 phagiis ; 2, the pyloric, placed behind the cardiac region. 



Around the pylorus is situated that extraordinary apparatus of hard 

 tubercles or sharp teeth which operate as grinding or tearing organs 

 on the food submitted to the action of this animal mill ; and though 

 the different pieces vary considerably in different species, their greater 

 or less development depending upon the nature of the food taken by 

 those species, they may be traced in all the Brachyura and Marroura. 

 In Squilla this masticatory framework is reduced to two half-liriiy 

 pieces, with rounded projections ; and, to make up for this deficiency, 

 a branch of each mandible reaches down to the pyloric orifice. 



From the pylorus the intestine proceeds direct to the vent, there 

 being no convolution ; but in the higher Crustaceans it is distinguish- 

 able into two portions, to which the names of duodenum and rectum 

 have been applied, and which are sometimes, in the lobster for in- 

 stance, separated by a valve, but more frequently are without defined 

 limits. In the lower Crustaceans the intestine in cylindrical, and 

 offers no difference throughout its whole length from the stomach to 

 the vent, which is always situated in the last ring, and has its orifice 

 closed by muscular fibres which perform the functions of a sphincter. 



The liver is largely developed in many of the Oriutacta, especially 

 in the Decapods ; indeed, no one can eat a crab or a lobster without 

 being struck with the large proportions of this vinous, which in those 

 species is considered so delicious. In the Edriophthalmians, on the 

 contrary, it is almost rudimentary, there being in them only three 

 pain of biliary vessels, much resembling those of insects. The organ, 

 when well developed, consists of two symmetrical portions, generally 

 separated from each other, and composed of a collection of ceecums, 

 which at one of their extremities discharge their secretion into excre- 

 tory ducts, which being converted by their union into longer and 

 larger vessels, pour the bile ultimately through a double channel into 

 the pylorus. The nature of the whitish fluid secreted by the two, 

 and, as it is said, in some cases three, elongated blind tubular worm- 

 like organs the first two situated on each side of the pylorus, and the 

 third on the middle of the intestine a short way below them U not 

 known, nor is its use. 



The two green glandular organs placed on each side of the 09*0- 

 phagus are supposed to act in some degree as substitutes for salivary 



expected, obMrrabU; certain part* of UM apparatus bdnc 

 into . probosoi. or tub* of longrr c 



Much has been written on the subject of the vascular system of the 

 Cnutacai. The following are the conclusions to which MiimMMwardn 

 and V. Audouin came, after a careful study, as well of the anatomical 

 disposition of the circulating apparatus of the Cnutatta, as of the 

 progress of the blood through its interior : 



" The circulation of the blood in these animals is accomplished in a 

 manner very similar to what takes place in the HoUiuca. The blood, 

 pushed forward by the heart, is distributed to every part of the body, 

 from whence it is returned into Urge sinuses situated at no great 

 distance from the base of the branchue ; from these sinuses it is sent 

 on to the respiratory apparatus, which it traverses, and from which it 

 finds its way to the heart, to recommence the same circle anew. The 

 heart is consequently aortic and single. The heart is always found 

 in the median line of the body, and lying over the alimentary canal, 

 near the dorsal aspect Its form is various ; in the Decapods it i 

 nearly square, and lies in the middle and superior part of the thorax, 

 being separated from the carapace by tegumentary membranes only, 

 and may be seen in the space included between the two vaults of the 

 flanks. In structure it appears to be composed by the interlacement 

 of numerous muscular fibres, fixed by their extremities to neighbouring 

 parts, and passing to some distance over the aggregate at either end, 

 o that the whole organ brings to mind such a figure as would be 

 irmed by the superposition of a number of stars the rays of which 

 do not correspond. In the other orders this general form of the heart 

 varies considerably, from the figure of an oblong square of rather 



considerable ate*, as it occurs in the Decapodn, to that of a long 

 cylindrical vessel extending through the whole length of the body, as 

 it appean in the Stomapoda and the Kdriophtlialmiflnit. In the 

 former of these it gives origin to six vascular trunks, three of which 

 issue from the anterior edge, and three from the posterior surface 



