Aug. 3, 1888.] 



SCIENTIFIC NEWS. 



in 



which must be shown under the microscope. It will 

 facilitate the demonstration if a piece of the vane of a 

 quill is soaked, first in alcohol, and afterwards in 

 glycerine. Cut out a small bit of the vane so prepared, 

 and tease it with needles as required. Notice the 

 different forms of the two sets of barbules which project 

 from every barb. One set bears hooks, the other is 

 simple or merely notched. The component parts of the 

 vane will be more readily understood if a bit of peacock's 

 plume, with disconnected barbs, is first thrown upon the 

 screen. The barbs and barbules will be clearly seen. 

 After this, it is easy to explain that in the close vane of 

 a quill the barbs lie parallel, each giving off at an open 

 angle close-set barbules. Every barbule crosses a 

 number of others belonging to the next barb, and at 

 every such crossing the uppermost barbule developes a 

 hook, which grasps the barbule beneath. Where the 

 hooks are absent, as in the tail-coverts of the peacock, the 

 feather, though it may serve for covering and ornament, 

 is useless for flight. 



Double-shafted feathers may then be described. The 

 accessory shaft (or after-shaft) has the same structure 

 as the principal one, and may be, as in the emeu, of 

 equal length. The primitive cylinder has been split 

 along two opposite lines, instead of one, to furnish the 

 double shaft and vane. The after-shaft is always turned 

 towards the body of the bird. Where the feathers serve 

 only for protection and warmth, as in large flightless 

 birds, it is easy to see the advantage of the double shaft. 

 Twice as many feathers can be crowded into the same 

 surface of skin. But this arrangement becomes im- 

 possible when the feathers are directl}' concerned in flight. 

 They must then admit of being rapidly spread, and also 

 of being neatl}' folded together when the wing is closed. 

 Accordingly, the quills of the wing and tail in a flying 

 bird never show a vestige of after-shaft. 



The pigeon may be used to point out the different 

 kinds of feathers, such as quills, body-feathers, down- 

 feathers, and filoplumes. These last are readily found 

 by plucking part of the breast ; they are very long and 

 thin, nearly devoid of vane, and without pith in the shaft. 

 Herons and some other birds have "powder-down 

 patches," consisting of peculiar feathers, which crumble 

 to pieces as fast as they are formed. 



The colours of feathers deserve some notice. Pig- 

 ments, similar to the pigments of hair, can be extracted 

 by a rather troublesome process ; the range of colours is 

 not very great, most of the effects being obtained by 

 shades of brown and yellow. Other colours, however, 

 occur, and some of them are very curious. The sealing- 

 wax tips of the Bohemian wax-wing are well known. 

 Still more singular is the Turacin found in the crimson 

 quills of the Touracos, or plantain-eaters. This pigment 

 is soluble in water, and washes off in heavy rain. Many 

 of the iridescent colours found in birds' plumage are not 

 due to pigments at all, but to light reflected from thin 

 films. They are due, in fact, to the same cause as 

 Newton's rings, the iridescence of mother of-pearls, or 

 the colours of the soap-bubble. 



Moulting is an interesting subject, which will bring 

 out the knowledge of observant naturalists. Professor 

 Newton's remarks in the article " Birds " {Enc. Brit. 

 vol. iii.) will serve as a basis for some preliminary ex- 

 planations. 



The development of the feather must on no account 

 be left out. It is essentially a horny scale, formed out 

 of the epidermis, like the scales of reptiles, but differs 



from these in being tubular below, and much divided 

 above, whereas the reptilian scale forms a broad plate 

 of simple form. A conical papilla of the dermis, or vas- 

 cular layer of the integument, supplies the growing 

 feather. The papilla is invested by a double layer of 

 epidermis, pushed inwards from the 

 outside of the body. Its surface is 

 marked by a branched system of sunk 

 lines, which correspond to the shaft, 

 barbs and barbules respectively, and 

 into this mould the nearly fluid cells 

 of the epidermis are forced. The 

 feather is, in short, a horny cast of 

 the surface of the papilla. At first 

 the vane surrounds the conical tip of 

 the cylindrical papilla completely, 

 but it is extremely thin along a line 

 opposite to the shaft, and here it 

 readily separates, opening out into a 

 flattish sheet as it becomes free from 

 the skin. The outermost epidermic 

 layer forms the sheath, which at 

 first adheres strongly to the quill, 

 but is free from the vane. When 

 a feather first pushes through the 

 skin, it is almost entirely hidden 

 within the sheath, from the summit 

 of which a pencil-like bunch of 

 barbs projects. Afterwards the sheath 

 crumbles entirely away. The apex 

 of the feather forms first, and may 

 be quite complete while the base 

 is still pulpy, or altogether undis- 

 tinguishable. Since the same part 

 of the papilla cannot be used a 

 second time as a mould for the deposit 

 of feather-substance, fresh growth 

 takes place at its base, and the apex 

 of the papilla is gradually pushed 

 upwards. In an immature feather, 

 the tapering and shrivelled tip of the papilla may often 

 be seen projecting from the umbilicus (see figure). 

 After its living substance has been absorbed, the papilla 

 is seen to consist of a chain of inverted conical capsules, 

 joined by a central filament. These cones may always 

 be found within the quill. After the vane has been 

 formed, the surface of the papilla becomes smooth, the 

 horny matter moulded upon it takes the shape of a 

 simple tubular quill, and the feather is complete. 



The Purification of Sewage. — MM. P. Chaotaing 

 and E. Barillot, in a communication to the Academy of 

 Sciences, state that irrigation, a system possessing 

 numerous partisans, is applicable where vast surfaces are 

 available, where the soil is suitable, and where the 

 water to be purified is not heavily loaded with putre- 

 scible matters. The chemical procedures, though much 

 decried some time back, deserve the greatest attention in 

 consequence of the improvements already effected, and 

 of those still possible. From the results which the 

 authors quote, it seems distinctly established that the 

 purification of sewage by chemical methods is really 

 efficacious ; that it can be applied without interruption 

 and without nuisance, and that the nitrogen and phos- 

 phoric acid thus obtained are easily available in agri- 

 culture. 



Diagram of a Feather. 

 s, shaft, cut short ; 

 /', bases of barbs ; 

 /, dried-up papilla, 

 projecting from the 

 umbilicus; p ', ditto 

 within the quill ; 

 q, quill. 



