REPTILES AND BIRDS. 
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INTRODUCTORY. 
THERE is little apparent resemblance between the graceful feathered 
warbler which makes the woods re-echo with its cheerful song and the 
crawling reptile which is apt to inspire feelings of disgust—between 
the familiar swallow, which builds its house of clay under the eaves 
of your roof, or the warbler, whose nest, with its young progeny, is 
carefully guarded by the father of the brood in the silent watches of the 
night, and the serpent which threatens them, its huge mouth disclosing 
fearful fangs, and against which the despairing parents have nothing 
but their slender bills to oppose. ‘‘ Placed side by side,” says 
Professor Huxley, “a humming-bird and a tortoise, or an ostrich 
and a crocodile, offer the strongest contrast; and a stork seems to 
have little but its animality in common with the snake which it 
swallows.” Nevertheless, unlike as they are in outward appearance, 
there is sufficient resemblance in their internal economy to bring them 
together in classifying the animal kingdom. ‘The air-bladder which 
exists between the digestive canal and kidneys in some fishes, 
becomes vascular, with the form and cellular structure of lungs in 
reptiles ; the heart has two auricles, the ventricle in most is imperfectly 
divided, and more or less of the venous blood is mixed with the 
arterial, which circulates over the body ; but, retaining their gills and 
being transitional in structure, they are also cold-blooded. _In birds, 
the lungs are spongy, the cavity of the air-bags becoming obliterated 
by the multiplication of vascular cellules ; the heart is four-chambered, 
transmitting venous blood to the lungs and pure arterial blood to 
the body; the temperature is raised and maintained at go° to 100° 
Fahr. 
Thus reptiles, like birds, breathe the common air by means of 
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