THE ANATOMY OF BIRDS. — SPLANCHNOLOGY. 209 



How sadly sweet the solemn strain — 



The dirge of the dying swan ! 

 That wondrous music, child of pain, 

 That requiem, sounding once again — 



And a bird's soul passes on. 



/. Splanchnology : the Digestive System. 



The Alimentary Canal, or digestive tract, is a tube which passes through the body 

 from mouth to anus, conveying food, the nutritious qualities of which are drawn off by the lac- 

 teals in transitu and assimilated, the refuse being voided. This is digestion. The canal is 

 really a tube within a tube, being contained in the cavity below the bodies of the vertebrae, 

 foi-med by the series of hcemal arches (p. 185). Birds are fast livers, their digestive operations, 

 like the processes of respiration and circulation, being very active and effectual ; they require 

 proportionally great quantities of food. The voracity of the cormorant is proverbial, but it is 

 probably not greater than that of the ethereal nightingale. Birds as a class are omnivorous ; 

 many species are as nearly omnivorous as any animals can well be ; but the majority are either 

 vegetarian or flesh-feeding. Very many birds feed upon fruits, hard or soft ; but even these, 

 when in the nest, are nourished for the most part upon the bodies of insects ; and it may be truly 

 said, that the great majority of birds are insectivorous. Birds seem to be the great controlling 

 agency in the economy of nature, of the increase of insect life ; agriculture would be difficult if not 

 impracticable without them, and their economic value is simply incalculable. Insectivorous 

 birds cannot be much interfered with, without destroying one of the most important and conse- 

 quential of nature's many beautiful adjustments. The bird cries perpetual " echec ! " to the 

 insect. Even those birds which are mainly flesh-eaters, as the hawks and owls, are similarly 

 beneficial, for the creatures they chiefly prey upon are the small rodents so fateful to husbandry. 

 The carrion-eaters contribute largely to make tropical regions habitable to man. Various 

 tribes of birds feed almost exclusively upon fish ; and these sometimes reach the dignity of 

 diplomatic and other political interests of mankind : nations have gone to war over the dung 

 of such birds, guano-beds being to some of the South American powers a large item of their 

 revenue. ChUi and Peru have been fighting lately, and the United States have been wrang- 

 ling, over the excrements of the alimentary canal of sea-birds. This tube, in general, is 

 shortest, simplest, and most direct in the flesh- and fish-eaters, the nature of whose food assim- 

 ilates already more nearly to the substance of their bodies than does that of the vegetarians. 

 The tube is modified in different portions of its extent, for the prehension, retention, saturation, 

 maceration, and comminution of food, and the mixture with it of other solvent fluids than those 

 secreted by the mucous membrane of the alimentary canal itself. Hence arise the various 

 modifications of its length, dilatation here, contraction there ; the presence in its lining mem- 

 brane of numerous follicles ; and the annexation of various glandular organs. Being always 

 longer than the body, the tube is necessarily coiled away in certain places ; this folding taking 

 place chiefly in the intestinal pai-t of the tract. Modifications of structure make recognizable 

 parts, as the mouth, gullet, crop, stomach, gizzard, intestine, cloaca, anus. Annex organs 

 are the salivary glands, the liver, and the pancreas, all of which pour their secretions into the 

 canal. This tube also receives the terminations of other systems of organs : the auditory organ 

 of special sense; the respiratory system, which is at first a mere bud or off-set from the 

 digestive ; the urinary and the generative, which, tliougli originally distinct, primitively and 

 permanently open into the lower bowel. Tlie intestiue is also continuous with the cavity of the 

 umbilical vesicle of the embryo, a primitive structure which disappears as the chick matures ; 

 and with that of the allantois, another embryotic organ which begins by budding from the intes- 

 tinal cavity. Its connection with the system of blood-vessels is direct through the lacteals and 

 tlioracic ducts (p. 199). Its operations are automatic and spontaneous, of the "reflex" order; 



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