94 



GAiNARIES, HYBRIDS, AND BRITISH BIRDS 



even of white. Tliis last occurrence, there- 

 fore, denotes a serious state of nlTairs, and 

 should be met at once by depict ie medicines, 



YY. 



BL 



WY 



The Egg and 

 its Structure. 



DIAGRAM OF AN EGG (MaKnified\ 



BL. Blast. . derm ; WV. While yolk; YY. Yellow yolk : V. Vitelline 

 inembrane ; F. Layer of very fluid albumen round the vitelline 

 meinhrane ; I). Dense albumen enelosine the yolk, with preceding 

 envelopes. In this envelope I) are incorporated the ends of CH, 

 the c>iala/.;v : W, Body of thi: albumen : C. Somewhat denser 

 layer of albiunen, sm rounded by a fluid layer ; M, M '. outer and 

 inner shell membrane, separated at A. air chamber : S., Shell. 



or it will probably be followed by the loss 

 of the liird. 



" IjCt us now consider the eg<f itself, 

 which is a much more com]>licated orifanism 

 than many people are aware 

 of. There is much even 

 in the shell, s [sec diagram |. 

 to e.xeite our interest. 



" It is composed chiefly of prismatic 

 particles [carbonate of lime, with a small 

 quantity of phos]ihatc of lime and animal 

 mucus, so arranucd as ti) allow of the 

 shell Ixiiig porous|. l'"or its tiiifkiicss and 

 texture its strenji'lh is ])hciiomcnal. 



" .\s hatching jjrocccds, howe\(r. tlu- 

 carbonic acid and dioxide fdi'mcil hv tlii' 

 breathing of the chick, dissohcd in Ihiitl, 

 gradually dissolve a portion of the material. 

 and thus the prismatic bodies are slowly 

 softened and ilisintcgrated. The shell thus 

 becomes far softer and more brittle as 

 hatching aiiproaches ; ami so great is Ihf 

 difference that if the eilgc of a liaclmf 

 made across a fresh egg-shell, and another 

 of one hatched or hatching, be examined 

 under a microscdpc. it will be inslanlly 

 seen th;d the two are in a (|iiitc dilTcreiit 

 molecular condition. Were it not fur this 



beautiful jirovision of Xaturc, the bird 

 could never break the shell. 



" The outer and inner shell membranes. \i 

 and m', separating the air-chamber, a. 

 need no further explanation. Proeeeding 

 inwards, we come next to the white or 

 albumen, w. This is composed of a denser 

 and a more fluid kind, arranged in layers, 

 which can lie peeled oil' in a hard-boiled 

 [fowl's] egg, like the layers of an onion. 

 A layer of the more fluid kind is always 

 next the shell, and another thin one, F, 

 next the yolk, but enveloped by another 

 layer, d, of the dense kind. If an egg be 

 broken into a basin, there will further be 

 observed attached to two opposite sides 

 of the yolk two slightly <)|)a(jue and rather 

 twisted thick cords, c ii, of still denser 

 albumen, termed the cluihr.d'. They are 

 not attached to the shell, but to op]iosite 

 sides of the dense layer of albiunen, d, 

 which envelops the inner fluid layer and the 

 yolk. They are so attached at opposite 

 sides, rather below the centre ; thus they 

 act as lialanciiig weights, keejung the 

 side of the yolk which carries the germ 

 always up])ermost. and very nearly in 

 floating equilibrium. If the egg be turned 

 round, therefore, the yolk itself does not 

 turn with it, but retains its position with 

 the germ on the u])]ier side. 



" It will be sct'ti how elaborately and 

 bi'autifidly the yolk, bearing upon its 

 upiK-r surface the tender germ, is protected 

 within the egg. Itself rather lightci- at 

 the upper part, it is fiirtlitr balaiifcd by 

 the clidhrji. st) as to lloat germ uppermost 

 in the albumi'ii. It is iisnalh' \ery slightly 

 liolilir tiiaii the alhiiiiieii. but sc.irctly 

 |((rcfi)tibly so: thus it lloats near the 

 iil)|ifr sitle of the slull. but always separ- 

 .•itfd from it b\' a layer of albumen of more 

 or less thickness, ami tiscillating gently 

 a\va\- from the shell on the least motion. 

 Ill a few cases it jirobably lloats more 

 slri)ii^l\- u]> anaiiisl the shell, and these are 

 generally llu' eases in wliiih aiihcrencc 

 takes ])lace. or the yolk is ruptured during 

 liatcliiiig ; but an i\t|iiisil tly tlelicate 

 lloat ing balance is the rule. Ne\ ertheless, 

 it will be readily uiulcrstood why it is 



