Reptiles and Birds. 



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 90 to ioo° 

 Fahr. 



Thus reptiles, like birds, breathe the common air by means of 



B 



