■/32 



General Characters.- 



-BIRDS.- 



-Genekal Characters. 



forming the ti'ue shaft of the feather, is sohd, and 

 composed of a white spongy substance coated with a 

 liomy slieath. It tapers gradually to the extremity ; 

 its lower surface exhibits a strong groove, whilst 

 its upper horny surface is iisually rather convex, 

 smooth, and continuous at the base, with the tubular 

 portion of Uie feather. At the pomt where the 

 upper homy sheath wrapping round the sides of the 

 stem forms the origin of the hollow quUl, there is 

 usually a second small stem, also fiuTiished with webs. 

 This, which is called the plumule, is not foimd in all 

 bh'ds, and where it does occur, is always confined to 

 the soft feathers forming the clothing of the body ; the 

 quill feathers of the wings and tail being destitute of it. 



The sides of tlie shaft are occupied by the webs, 

 composed, as already stated, of mmierous flattened 

 fibres or barbs. These are inclined towards the apex 

 of the feather. They are usually concave in front and 

 convex behind ; so tliat they fit together very closely, 

 and their mutual adhesion is provided for by the 

 agency of a series of minute secondary fibres, or 

 larhulcs, which spring from their margins. These 

 characters are not, however, common to all the barbs 

 even of the same feather. The lower barbs are usually 

 soft and disunited, forming the substance well known 

 as down, and in many of the feathers clothing the 

 body tills downy portion constitutes the principal part 

 of the feather, thi^ tip only being formed by a few stiff 

 barbs. The accessory plumide, where it exists, is 

 always of a do\vny nature, and in a few species of 

 birds the whole plumage shows a tendency to acquire 

 a similar structure. The sldns of many birds, espe- 

 cially of the aquatic tribes, are also clothed, beneatli 

 the ordinary covering of feathers, with a thick coat 

 of do'W'n, which, although evidently analogous in its 

 nature to the true featliers, yet exhibits certain pecu- 

 liarities desemrig of special mention. The down 

 consists of a multitude of minute tubes inserted into 

 the skin, from the extremity of each of which there 

 arises a little tuft of soft, disunited filaments. These 

 may eiadently be regarded as the barbs of a shaftless 

 feather, and they are furnished on each side with 

 luunerous minute fibres representing the barbules. 



In all birds the feathers are changed once or twice 

 in tlie course of the year, the old featliers falling out 

 by degrees, to be replaced by new ones. This process 

 is called itioulting. In it, as m the first clothing of 

 the bird with its feathers, these organs are foimed in 

 small tubes in the skin, lined by a duplicature of the 

 epidermis. A peculiar fluid secretion is produced at 

 the bottom of each tube ; this is soon inclosed in a 

 delicate, conical, horny sheath, with its point directed 

 outwards ; and within this sheatli the formation of the 

 feather goes on. As the latter increases in size, the 

 point of its sheath is extended towards the surface of 

 the skin, from which it finally issues, and then, burst- 

 ing, allows the inclosed feather to make its escape. 

 The portion of the formative fluid remaining in tlie 

 quiU after the feather has attained its maturity, is 

 gradually dried up withm tlie cavity, where it forms 

 tliat peculiar membranous substance which every one 

 must have observed in the quills destined for use 

 as pens. 



In the bats, the only foiTns of mammals which are 

 endowed \\A\h. the power of flight, the function is per- 

 formed, as has aheady been stated, by the agency of 

 broad membranes, which, when they are extended 

 by the elongated fingers, constitute admirable organs 

 for aerial locomotion. In tlie bats, also, the tail is 

 usually provided with a membrane of gi'eater or less 

 extent, which is of great ser\'ice to these creatures in 

 directing then- course through the air. In birds the 

 same purposes are fulfilled in a very different manner, 

 but still by an extension of the tegument-aiy appen- 

 dages. The structure of tlie anterior member in a 

 bird, as already described (see Plate 3G), is very differ- 

 ent from that of tlie same part in a bat. For all 

 practical purposes, tlie region of the hand may be 

 regarded as reduced to a single finger, so that the 

 limb forms a single series of long joints placed end to 

 end. But the feathers implanted in the skin of these 

 members are of large size and firm texture, and so 

 arranged that when the mng is extended the}' spread 

 out like the rays of a fan, so as to expose a broad 

 surface to tlie air ; whilst by the mode in which they 

 mutually assist eacli other, and their o^\'n proper 

 elasticity, tlieir power of resistance is very considerable. 

 At the same time, when the wing is closed, they pack 

 together mto a comparatively small compass, and are 

 thus no impediment to their owner in movhig about 

 upon the ground or in trees. 



As the number, form, and arrangement of the quUl 

 feathers of the wing are of considerable importance in 

 the classification of birds, ornithologists have found it 

 necessary to give diem different names, accordmg to 

 tlie region of the wing upon wliich tliey are situated. 

 The longest and strongest, and consequently tliose 

 which have the most influence upon tlie power of flight 

 possessed by any bird, are the featliers inserted upon 

 the hand ; these are called primaries. They usually 

 decrease m length from die outer margin of die wing, 

 and in diis case the wing is more or less pointed in its 

 outline ; in other cases the longest feather is die fourth 

 or fifth, when the apex of the wing becomes more or 

 less rounded. Their number is usually nuie or ten, and 

 sometimes eleven. The name of secondaries is given 

 to the feathers attached to the middle division of die 

 anterior limb, corresponduig with the fore-arm of man; 

 these are shorter and weaker than the primaries, and 

 vary far more in dieir number. The tertiaries are the 

 featliers attached to the arm. A few small quill fea- 

 thers attached to the rudimentary thunib, form what is 

 called the alula, or spurious wing, and the bases of all 

 the quiUs are concealed by numerous large but com- 

 paratively soft feathers, foiTning the wing-coverts, which 

 are distinguished as primarj' and secondary, according 

 to their position. 



The quill feathers of the tail, hke those of the wuigs, 

 are long and stiff; they are furnished with muscles, by 

 which they can be spread out to catch the air or con- 

 tracted within a small compass, and by the motion of 

 the tail itself they may be tm'ned in various directions. 

 Hence, from dieir serving in some sort as a radder for 

 die bird in its aerial course, they have been termed 

 rectrices; the quills of the wings being also kno^^Tl as 

 remigcs, from their being the main instruments of pro- 



