i86 EGGS 



that when the bird has attained her full vigour improvement stops, 

 and a few years later the intensity of hue begins to decline. It 

 would be well if we had more evidence, however, in support of this 

 opinion, Avliich is chiefly based on a series of eggs of one species — 

 the Golden Eagle, Aquila chrysaehis, in the A^nriter's possession, 

 among which are some believed on good grounds to have been the 

 produce in the course of about twelve years of one and the same 

 female. The amount of colouring-matter secreted and deposited 

 seems notwithstanding to be generally a pretty constant quantity — 

 allowance being made for individual constitution ; but it often 

 happens — especially in birds that lay only two eggs — that nearly 

 all the dye will be deposited on one of these, leaving the other 

 colourless ; it seems, however, to be a matter of inconstancy which 

 of the two is first developed. Thus of two pairs of Golden Eagles' 

 eggs also in the possession of the writer, one specimen of each pair 

 is nearly white while the other is deeply coloured, and it is known 

 that in one case the white egg was laid first and in the other the 

 coloured one. When birds lay many mottled, and It fortiori plain, 

 eggs, there is generally less difference in their colouring, and though 

 no two can hardly ever be said to be really alike, yet the family- 

 resemblance between them all is obvious to the pi'actised eye. It 

 would seem, however, to be a peculiarity with some species — and 

 the Tree-SPARROW, Passer montanus, which lays five or six eggs, 

 may be taken as a striking example — that one egg should always 

 differ remarkably from the rest of the clutch. In addition to what 

 has been said above as to the deposition of colour in circular spots 

 indicating a pause in the progress of the egg through one part of 

 the oviduct, it may be observed that the cessation of motion at 

 that time is equally shewn by the clearly defined hair-lines or 

 vermiculations seen in many eggs, and in none more commonly met 

 with than in those of most Buntings, Emherizidx. Such marldngs 

 must not only have been deposited while the egg was at rest, but 

 it must have remained motionless until the pigment was completely 

 set, or blurred instead of sharp edges would have been the residt.^ 



^ The priucipal oological works witli coloured figures are the following : 

 Thienemann, Fortpflanzungsgeschichte dcr gesa7nmten Vogel (4to, Leipzig : 1845) ; 

 Lefevre, Atlas des cevfs des oiseaux d' Europe (8vo, Paris: 1845); Hewitsoii, 

 Coloured Illustrations of the Eggs of British Birds (8vo, Ed. 3, Loudon : 1856) ; 

 Brewer, Noi-th American Oology (4to, Washington : 1859) ; Taczanowski, Oologia 

 JPtakdw Polskich (8vo, Warszawa : 1862) ; Badeker, Die Bier der Europdischen 

 Vogcl (fol. Leipzig : 1863) ; WoUey, Ootheca Wolleyana (8vo, London : 1864) — 

 some of which have never been completed. The above is not, and does not 

 profess to be, an exhaustive list, and perhaps some others deserve inclusion in 

 it ; but there are works, chiefly on British oology, which have unfortunately 

 attained considerable notoriety, though really unworthy of serious notice, either 

 from the recklessly inaccurate statements to be found in the text which accom- 

 panies the plates, or the misleatling tendencies of the plates. I prefer passing 



