BIRDS. 203 



inense distance. Their tongue being chiefly of bone or cartilage, 

 they have little delicacy of taste ; and the sense of touch, judging 

 from the structure of their claws and beak, which would be the 

 organs for its exercise, must be exceedingly imperfect. 



Most birds construct nests, and some of them with much 

 care, labor, and ingenuity. In these they deposit their eggs, and 

 hatch them by the heat of their own bodies. Some few lay them 

 upon the sand, and leave them to be hatched by the heat of the 

 Bun. Their care and affection for their young are well known, and, 

 in providing for and protecting them, they exhibit many indica- 

 tions of sagacity or of feeling. They are capable of some slight 

 improvements by education and imitation, but are, on the whole, 

 in this respect decidedly inferior to quadrupeds. The class of 

 birds is divided, according to their structure and habits of life, 

 into six orders. 



Birds shed their feathers at regular periods. This operation 

 is called mouitmg, ana is performed by Nature in the following 

 manner : The quill, or feather, when first protruded from the skin, 

 and come to its full size, grows harder as it grows older, and re- 

 ceives a kind of periosteum or skin round the shaft, by which it 

 seems attached to the animal. In proportion as the quill grows 

 older, its sides, or the bony pen-part, thicken ; but its whole dia- 

 meter shrinks and decreases. Thus, by the thickening of its sides, 

 all nourishment from the body becomes more sparing ; and, by the 

 decrease of its diameter, it becomes more loosely fixed in its socket, 

 till at length it falls out. In the mean time, the rudiments of an 

 incipient quill are beginning below. The skin forms itself into a 

 little bag, which is fed from the body by a small vein and arteiy, 

 and which every day increases in size, till it is protruded. While 

 the one end vegetates into the beard or vane of the feather, that 

 part attached to the skin is still soft, and receives a constant 

 supply of nourishment, which is diffused through the body of the 

 quill by that little light substance which we always find within 

 when we make a pen. This substance, which as yet has received 

 no distinctive name, serves the growing quill as the umbilical 

 artery does an infant in the womb, by supplying it with nourish- 



