STOMACH AND INTESTINE. 



295 



The reader will, however, observe, that the is aided by a dental apparatus, in the shape 



title of the following article does not announce 

 an essay on the process of digestion, or the 

 various organs which effect it; but limits itself 

 to two portions of the alimentary canal, 

 hitherto undescribed in this work. But it is 

 impossible to treat of the functions of the 

 stomach and intestine except in connection 



of a hollow cylinder enclosing long teeth, 

 as in the genus Napula. 



The Rotifera are so named from the cur- 

 rents produced by their prehensile cilia i 

 which are here limited to groups surrounding 

 the mouth of the animal. 



Many of them have an organ of mastica- 



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with the entire process in which they take so tion. This usually consists of three pieces : 



large a share. \Vhile the numerous observa- each of the two facets of a kind of anvil being 



tions and researches which have been made worked upon by the rough or toothed terminal 



since the appearance of the earlier article surface of a recurved jaw, the longer limb of 



DIGESTION require some notice in the which receives a muscle at its extremity. 



Supplement of which the present essay forms The intestinal canal generally exhibits a 



apart. For these reasons the author has felt pharyngeal enlargement, which is followed 



it advisable not to confine himself too strictly by a narrow "oesophagus," of varying length, 



to the exact limits uhich the heading " Sto- 

 mach and Intestine'' might seem to imply. 

 Hence, though the following essay will treat 



ending in a wider "intestine." In the 

 Gasterodela a dilatation, called a stomach, pre- 

 cedes the intestine. In the Rotifer vulgaris 



chiefly of the above segments of the alimentary and others, an almost globular enlargement of 

 canal, it will also comprise a very brief account the narrow canal is so immediately followed 



of whatever is at present known concerning the 

 w hole digestive act. Commencing by a rough 



by the constricted cloaca, as to have been com- 

 pared to a large intestine. The organ of 



sketch of the anatomy of these parts in the digestion is also often complicated by the 



animal kingdom, we shall successively consider, 

 their structure and functions in the human 

 subject ; their relation to digestion and nutri- 

 tion ; and finally, their appearances in disease. 

 COMPARATIVE ANATOMY. In the Infuso- 



presence of blind tubes ; which vary, not 

 only in number and size, but also in posi- 

 tion, and possibly in import. Thus they may 

 open, either into an uniform and narrow canal, 

 or into the commencement of the intestine, 



ria, whose minuteness places them at the or into the presumed gastric dilatation ; or, 

 lowest extremity of the animal kingdom, the c ~~ "' " 

 organ of digestion has already attained such a 

 development as to form the chief basis of 

 their nomenclature. 



One or two genera present us with a rare 



finally, as in the Digltena lacustris, a set of such 

 tubes may occupy both of these latter situa- 

 tions. 



The various members of the order Entozoa 

 are grouped together in obedience to a cla.ssi- 



and exceptional condition : viz. the absence fication which is here and there arbitrary and 

 of all traces of digestive cavity. Such are the anomalous, but in the main both natural and 



useful. It offers three chief varieties of the 

 digestive organ, all of which are very inte- 

 resting. 



a. In many as in the Echlnococd 

 and their congeners no trace of a special 

 digestive cavity is present. Without mouth, 

 stomach, or intestine, the creature floats free 



parasitic Gregarina and Opalina ; in whom, 

 as in some of the Entozoa, digestion and 

 absorption appear reduced to a simple phy- 

 sical process of endosmose, which carries 

 the nutritious substances dissolved in the 

 fluid medium they inhabit at once into the 

 mass of their corporeal juices. 



The Poh/gristria possess a plurality of in the cavity of its enclosing cyst, or buries 

 stomachs or internal sacs ; and the relations its barbed head in the tissues of a living 

 of these to the intestine, together with the con- habitation; whose juices, thus brought into 

 dition of the latter tube, subdivide this group relation with its exterior, are applied to its 

 into numerous families and genera. Thus nourishment by what seems to be rather a 

 many are named "anenterous," because they process of endosmose than of digestion pro- 

 appear to be devoid of intestine. Of these the perly so called. 



Monas termo which has four or five globular /3. In other genera belonging to the Cestoid 

 stomachs, of 5TT jL_^th of an inch in diameter, and Trematoid divisions, there is, however, 

 appended immediately to its mouth may be a canal, which is apparently related to digestion, 

 taken as the type. Others possess similar and the main features of which repetition 

 sacs in connection with a simple Intestine ; and ramification may be represented by the 

 and are chiefly distinguished by the straight, Teenia and Distoma respectively, 

 curved, or wavy course of this canal, or by For example, in the Tape- worm, a minute 

 the single or double character, and lateral or mouth opens into a slender tube, the bifurca- 

 terminal position, of its apertures. Most of tions of which reach the margins of the body 

 them devour a living prey of kindred Infuso- where this begins to assume its regular jointed 



form. From hence onwards the canal might be 

 compared to a ladder, with rungs at the fore 

 and aft extremity of each joint, at the 

 right angles of which its longitudinal and 

 transverse branches unite. It is probable that 



ria; prehension being often visibly effected 

 by cilia, the voluntary action of which 

 carries a current of food into the mouth, or 

 removes egesta by a simple reversal of the 

 stream. And sometimes this act of ingestion 



ordinarily sufficient, are capable of being locally- 

 exhausted by the excessive demands of a particular 

 clo^s or specie*, and renewed by an artificial supply. 



these canals possess valves. But whether 

 tney have any constant or valid terminal ori- 

 fices seems doubtful. 



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