HARD WICKE' S S CIENCE- G O SSIP. 



55 



Now I am going to bring before your notice some 

 simple feathers, tell you their uses and their struc- 

 ture. Perhaps it may seem ridiculous to write about 

 ■such seemingly simple things, but you will form your 

 own opinion afterwards. I do not promise you an 

 easy task to understand them; but if I succeed in 

 showing that the simplest items of God's handicraft 

 are not despicable as a study, you and I will be well 

 repaid for our time. 



Uses, etc. — Feathers are, as you know, a very cha- 

 racteristic feature of all birds. It was in consideration 

 of this fact that Blainville proposed to name the sub- 

 ' kingdom of birds (aves) Pennifcres. It would be 

 foolish for me to attempt to describe how a bird flies, 

 for in a minute or two by careful observation you can 

 learn more than I can write in two pages. It is 

 sufficient to say that when the wings are outspread 

 they expose a broad surface to the air, so that the 

 bird can either float with the wind, or by convenient 

 movements of them make headway against it. The 

 long feathers of the tail are used as a sort of rudder 

 to assist the bird in steering to its destination. 



You will see how handy the wings work if you call 

 to mind the membranes of a bat. Although a bat 

 can fly, and the membranes are strong and resist the 

 air well, it cannot pack them as neatly as a bird can. 

 Wings offer a considerable resistance to the air, 

 expose a large surface, and can be retracted and 

 packed in small room on the sides of the body, so 

 that they are no impediment to walking on terra 

 firma. 



Feathers are non-conductors of heat, and help to 

 keep the high temperature of no° F. normal in 

 birds. The normal temperature of mammals is 

 ioo° F. By an ingenious arrangement air does not 

 pass at all readily through feathers, especially those of 

 the wings and tail, which is a considerable advantage 

 in flight. In some species of birds, especially aquatic 

 birds, it is desirable that their feathers should resist 

 the passage of water. This is secured by the act of 

 " preening," in which the feathers are anointed (by 

 the passage of the feather through the mouth) with 

 an oil got from a sebaceous gland, termed the tcro- 

 pygial gland, situated at the posterior end of the 

 body. This gland opens to the exterior by two 

 apertures situated on elevated pieces of flesh. 



Moulting or changing of feathers occurs once or 

 twice a year. The old feathers gradually either 

 become loose and drop out, or are plucked out by the 

 bird, their places being supplied by new ones. It 

 will perhaps be convenient here to sketch the 

 formation and development of a feather. 



Development. — The external skin first becomes 

 pitted in, and the mouth of the pit closed by the 

 adherence of its sides. Thus you have a tube- 

 shaped cavity lined with epidermis synchronous to 

 that on the outside. A fluid is now secreted at the 

 base of this sub-epidermal tube and becomes enclosed 

 in a sheath of a horny texture, pointing to the exterior. 



The feather is formed in this laboratory, as we may 

 call it, and after having approached very near the 

 surface and burst, the juvenile feather makes its 

 way out and soon arrives at maturity. As the 

 feather is formed from the formative fluid, this fluid 

 dries up and remains as the membraneous substance 

 found in the interior of the feather. 



Varieties. — Feathers differ both on different birds 

 and on different parts of each bird. Thus they have 

 served as a basis for classification. Examples of 

 various kinds of feathers on different birds are easily 

 met with, as those of the ostrich and goose. Notice 

 how brilliant are the colours of some birds, as 

 humming-birds, lyre-birds, or even the canary, in 

 comparison with the sober-clad hedge-sparrow, thrush, 

 etc. Some species of birds have all their feathers 

 downy. Thus feathers vary on different birds in 

 structure, colour, and texture. Singular things are 

 found on some birds, as the herons, called poivder- 

 do'din patches ; these are caused by the tops of feathers 

 of a peculiar downy nature, breaking down to powder 

 or dust as fast as they are produced. 



As before stated, feathers are of various kinds on 

 the same bird. If you examine a bird, such as the 

 hen or pigeon, you will see that a certain class of 

 feathers cover the body generally, head, neck, breast, 

 etc. These are termed contour feathers, or penncc. 

 In other parts of the body, i.e. the wings and tail, 

 you find feathers of a much stronger and larger 

 build, these are the quill feathers. Those on the 

 wings are termed remiges, and are subdivided into 

 primary or secondary, according to their position. 

 The tail feathers are called rectrices, and are some- 

 times arranged in a grotesque but beautiful fashion, 

 as on the peacock or lyre-bird. Small feathers cover 

 the somewhat ungainly insertions of the quills, called 

 coverts, as their function implies. 



If you had to pluck the bird in the ordinary way, 

 you would notice two things. Firstly, that there still 

 remained on the bird small downy feathers, which are 

 filoplumes. Their peculiar structure I shall note 

 afterwards. Secondly, that the feathers were crowded 

 in some parts of the integument, while on others they 

 seemed more or less scarce. The covered areas are 

 called pterylea, the uncovered areas apteria. 



Structure. — An individual feather consists of a 

 quill prolonged into the rachis, which gradually 

 tapers to one extremity ; from this rachis arises on 

 each side a series of processes called barbs, and 

 from the barbs, and at right angles to them, arise 

 a diminutive set of processes termed barbules. The 

 ingenious structure and uses of these barbules is 

 the most interesting feature about a feather. The 

 barbs are thin like paper and curved, the convex 

 curve being nearest the insertion of the feather. 

 The barbules are arranged in two rows, one on 

 each side of each barb. It is a difficult thing to 

 describe their exact position, but a T" represents 

 it roughly, the two horizontal limbs corresponding 



