CHAPTER IV. 



THE INCXTBATIOX OF BIRDS. 



Many will not hesitate to adt)pt the words of the poet : — 



■• It wins my admiration 

 To view the stiuctm-e of that little work — 

 A bird's nest. JInrk it well, within, without : 

 Xo art had he that wrought ; no knife to eut, 

 No nail to fix, uV) bodkin to insert. 

 No glue to join — his little beak was all ; 

 And yet how neatly finished ! What nice hand, 

 With every complement and means of art, 

 And twent}- years' apjirenticeship to boot. 

 Could make me such another? Fondly, then, 

 ' We boast of excellence, whose noblest skill 

 Instinctive genius shames." ' 



The exquisite structures, which we shall hereafter illustrate, are attributable to the 

 one essential particular -^-hich distinguishes the feathered tribes from the mammalia, 

 in their beiiig o\'i23arous ; that is, instead of producing their young full}' formed, thej' 

 lay eggs covered with a hard calcarous shell, which contain the embryo, requiring a 

 certain degree of warmth for its future de\elopment. This being duly applied — 

 generally by the assiduous parent brooding over the nest — the young burst from their 

 imprisoned state, and enter on a new existence. But here are various processes of great 

 interest, on which it will be desirable briefly to dwell. 



The egg-organ of a bird contains all the eggs which are to be laid during several 

 years, among which dift'erenceS are observable in substance, colour, and size. Those 

 which are to be first laid, are largest and of a yellowish hue ; the others are graduall}^ 

 less in size and lighter in colour. At first, the egg appears as a small yellow globe, but 

 it increases in size till it drops from its slender fastening, and falls into the egg-tube. 

 Before it does so, it has neither white nor shell, and without the latter, eggs are some- 

 times laid from accident, or from the bird being in ill-health. 



On falling into the tube, the egg has only a single and very thin membrane for a 

 covering, but one that is a little thicker soon succeeds. This is produced by the egg- 

 exciting (he vessels lining the tube to throw out a substance, which forms this second 

 coating, jutting into small knobs at each end. As the egg passes along, it is also thickly 

 covered with the white that fiUs the tube ; and proceeding onward, it obtains a third 

 coating, which is the first layer of the membrane of the shell. Over this, the second 

 layer is formed, and as the egg proceeds through the remainder of the tube, the shell is * 

 completed. The growth of an egg is exceedingly rapid ; and with the white and the 

 shell it is particularly so. 



4' 



Hui'dis. 



