8TOMATODA. 



STOMAPODA. 



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digestion. In different parts of the stomach, and at different time*, they 

 vary in the nature of we substance which they contain ; and it seem* 

 probable that theae variation* depend on whether the tubes are, or are 

 not, engaged iu producing digestive fluid. Those which are ao occupied 

 are completely filled with cells in different stages of development; 

 those which are inactive are empty, and have their walls lined inter- 

 nally by epithelium, similar to that which invests the interior of the 

 stomach. In the production of the cells containing the digestive 

 fluid, small granules ore first generated in the deeper part of each 

 tubular gland : these, coalescing by twos or threes form nuclei, on 

 which the cells ore developed according to the ordinary mode of for- 

 mation of primary cell*. The cells are of an oval form, about l-2000th 

 of an inch in length ; and, as fast as they are produced, they are pushed 

 towards the orifice* of the tubes, from which, while digestion is going 

 on, they are discharged iu such numbers as to form, with a small 

 quantity of fluid separated at tho same time, the thick layer of mucous 

 by which the whole interior of the stomach is lined, and by which the 

 portions of food are invested. In the intervals between successive 

 act* of digestion, it seems probable that the orifices of the tubules 

 are closed by small portions of epithelium similar to that by which 

 they are lined, and which are elevated and broken through for the 

 discharge of the cells as soon as the active process commences. 



During digestion there are also often found, just beneath the surface 

 of the mucous membrane, around either the cardiac or pyloric orifice, 

 and along the lesser arch of the stomach, a number of small closed 

 sacctili, filled with an opaque white fluid containing cells, which, when 

 their contents are matured, burst and discharge them into the interior 

 of the stomach. But tho exact office of these bodies (which have 

 been generally described as the gastric follicles, or lenticular glands of 

 the stomach) is not known ; they are certainly not always present, 

 but probably ore produced rapidly while digestion is going on, and, 

 having discharged their contents, ore again rapidly absorbed. [INTES- 

 TINES; DIGESTION; FOOD.] 



8TUMAPODA. M. Milne-Edwards comprises in the order Sloma- 

 poda all the Podophthalmous Cruttacea which are deprived of thoracic 

 bronchia) lodged in internal cavities. 



This division is entirely composed of Swimming Crustaceans, whose 

 body is elongated, and whose general form often approaches closely to 

 tbnt of the Macrouroun Decapods ; but in those animals the concen- 

 tration of the rings of the head and thorax is carried less for. In the 

 greater part of the Stomajmla the ophthalmic and antennular rings 

 are not confounded with the rest of the head, and they even sonic- 

 times acquire a remarkable development^ As in the other Podopli- 

 Ifinlma, there always exists a Carapace, which is formed by the 

 enlargement of the dorsal arch of the antennary or mandibular rings ; 

 but the dimensions of this buckler vary greatly. Sometimes it covers 

 nearly the whole of the thorax, and only leaves exposed a portion of 

 the last ring of that part of the body ; sometimes, whilst it prolongs 

 itself above the thoracic rings, it only adheres to those which are 

 near the mouth, and leaves the others free and complete under its 

 lower surface. In other cases it does not reach the four or five hist 

 rings of the thorax, which then resemble those of the abdomen. In 

 form it varies too much for general description. The Thorax is 

 generally elongated, and entirely composed of segments moveable 

 upon each other. Sometimes all tho rings of this port of the body 

 are united into a tingle piece. Tho conformation of the Abdomen 

 varies still more ; this portion of the body presents in general nearly 

 the same disposition as in the Macrourous Decapods, and terminates 

 by a grrat caudal fin composed of appendages of the sixth ring and 

 the following segment; but in some Stouiapods the abdomen is 

 rudimentary. The disposition of the limbs is equally variable. The 

 Eyes are always carried on a first pair of moveable appendages, the 

 length of which is often very considerable, and whose disposition is 

 essentially the same as in the Macrourous Decapods. The first pair 

 of Antenna! an rather long, and terminate in two or three multi- 

 articulate filaments ; their peduncle is always cylindrical, and they 

 can never be bent back under the front as in the lirachyurous Deca- 

 pods. They are inserted below the eyes, near the median line, or 

 externally to the base of those organs. The second pair of antenna 

 vary still more; their conformation however generally approaches 

 that in the Crangonida. The builary joint of their peduncle nearly 

 always carries above a great ciliated blade, and they terminate by a 

 long multiarticulate filament. In the greater part of the Stomapods 

 they are inserted ouUide the first pair, nearly on the same trans- 

 venal line. The distance which separates the mouth from these 

 appendage* is generally very considerable ; and tho carapace never 

 recurves below, so as to form round that aperture a well determined 

 frame serving to lodge the jaw-feet, as in tho greater part of the 

 Decapods. In the majority the buocal apparatus is more simple than 

 in the preceding order, and is only composed of an upper lip, a pair 

 of mandible*, a lower lip, two pairs of jaws, and a single pair of jaw- 

 feet; the** last organs an either altogether wanting, or an trans- 

 formed into natatory feet, and nearly always the seven following pairs 

 of liiuba an all so formed a* to constitute natatory or prehensile 

 feet. It is also worthy of note, that in the Stomapods the second 

 pair of jaws never carry at their bate a lamellar appendage analogous 

 to the valvule, which, in the Decapods, fulfils functions so important 

 in the mechanism of respiration ; and this modification of structure 



it a natural consequence of the absence of a respiratory cavity which 

 includes the thoracic bronchia, os in the preceding order. 



Then on generally seven or eight pairs of Feet, often presenting 

 the same mode of conformation. They are nearly always provided 

 with an appendage, which may be considered as the analogue of a 

 palp. Then is often found also at the base of many of the anterior 

 feet another soft and vesicular appendage, which has sometimes the 

 form of a galette, and which represents the flagrum, an organ which, 

 in the greater portion of the Decapods, is lamellar and of a horny 

 consistence; but which, in certain Shrimps, presents a structure 

 similar to that in tho Stomapods. Thne of the last pain, or a greater 

 number, on always natatory ; tho first pair, or even the first four, an 

 often prehensile ; but they never terminate in a didactylous pin < r. 

 as in the Decapods : they an subcheliform, that is to say, nothing 

 more than a moveable claw which falls on the preceding joint. The 

 greater part of these organs an approximated to the mouth, or even 

 applied against it ; a disposition which has been the cause of the 

 appellation Stomapods. The abdominal members present nothing 

 peculiar ; their number is nearly always six pairs. 



The Bronchia; of the Stomapods are always external, and present 

 in general a more complicated structure than those of tho Decapods. 

 Instead of being composed of lamella;, or simple filaments, they an 

 framed of cylinders ranged in parallel order, giving origin to other 

 smaller cylinders, which, in their turn, ore equally fringed. Some- 

 times these ramose branchial ore fixed at the base of the thoracic 

 feet, and suspended under the thorax ; but in general they spring 

 from the baailary joint of the abdominal false feet : in some of tho 

 order they are reduced to a rudimentary state ; in others nothing is 

 to be seen which can be considered as a special organ of respiration ; 

 and, in such cases, there is every reason to believe that this function 

 is exorcised by the general surface of the teguments. 



2 



Branchim of Stvmapoda. 



1 , one of the branchltr of Thytnnopoda : a, base of the posterior foot ; 6, 

 branchiEC ; c, palp. 



2, a branch!* of Sqwlla : a, bane of the false foot ; I, branchia ; r, i, the two 

 terminal branches of the false foot. 



3, a, one of the branches of thl* ramose branchia; b, the branchleti 

 (ramuscle*). 



4, one of the abdominal false feet of Cynthia : a, boiilarv joint ; b, branchia ; 

 , lamellar appendage*. 



The apparatus of Circulation differs much from that of the Deca- 

 pods. In the f'tuillir, the only Stomapods which have been anatomi- 

 cally examined, the heart, instead of being nearly quadrilateral, "M.I 

 situated towards the middle of the thorax, bos the form of a long 

 cylindrical vessel, which extends throughout tho length of the abdo- 

 men ; the arteries which spring from thin tubular heart are distributed 

 in a peculiar manner ; and the principal venous sinuses, instead of 

 being situated on the thorax, occupy the abdomen. 



The Stomach of some Stomapods presents vestiges of the solid 

 framework, which, iu the Decapods, is armed with teeth serving to 

 bruise the aliments in the interior of the digestive cavity ; but in 

 general nothing similar is to be found. The structure of the Liver 

 also varies; and in those species in which the organs of generation 

 have been examined, nmarkable peculiarities have been observrd in 

 their disposition. The Nervous System in this order presents also 

 modifications which have not been found in the Decapods ; but its 

 disposition varies too much to enable M. Milne-Edwards to say any- 

 thing general of it. 



M. Milne-Edwards divides the Stomapoda, after the example of 

 Latreille, into three families : the Caridoides, tho Bicuirosids and 

 the Unicuirasscs. 



I. Coridoid Homapoda. 



The Crustaceans arranged by M. Milne-Edwards under this family 

 bear a close resemblance in their general form, he observes, to tho 

 fomily of Salicoques; and indeed till lately their position had In en 

 in the order Dtcapoda, when they constituted a small and pcculi.tr 

 family under the name of flbftssWMM. 



Tho body in thick, and slightly compressed laterally. Head con- 

 founded with the thorax, and all the rings of the lost-name! 

 (with the exception, sometimes, of the last, or of the last two) com- 

 pletely united together and soldered above with the carapace. Abdo- 

 men considerably developed, and terminating by a great fin composed 



