30 



THE FEATHERED IKTBES. 



A vesicle is now so for formed as to have passed from the body of the chick to the lining 

 membrane of the shell ; and, as the embryo grows, so does tliis vesicle increase. It is 

 fidl of blood-Acssels — a living system of arteries and veins — carrying livid rod blood from 

 the body of the chick, and retiu-ning it of a bright red colour, perfectly titled for every 

 pui-pose it is designed to answer. 



About the sixth day, the bare wings and logs of the chick may be fully seen ; the eyes 

 are large and prominent ; the brain begins to acquire consistence, and, a little later, the beak 

 opens for the first time. The additional growth of a few daj-s shows the wings and tlic 

 body covered with short feathers ; and that which, a short time before, was a shapeless 

 mass, has now ibrm, proportion, and organic life. 



So soon, however, as the beginning of the third day, the beating of the heart is per- 

 cejitible, though no blood is A'isible. But only a few hours elapse, and two vesicles, 

 containing blood, appear, one tbrming the left ventricle, the other the great artery. The 

 auricle of the heart is now seen ; and the ^VTiter will never forget the pleasm-e with 

 wliich he first saw an egg at this stage of developing the chick, exhibiting, as it did, the 

 coiu-se of the blood to the imassisted eye. If an egg be opened between the twellth and 

 thirteenth day, the jjulses of the numerous blood-vessels will be seen propelling onwards 

 their contents, and tluis presenting a very remarkable and beautiful sjiectacle. About 

 the fifteenth da}', the yolk-bag begins to be received into the body of the chick, as is 

 also the white. 



As on the eighteenth day the faint piping of the little tenant of tlie shell is heard, 

 respii'atiou.has alrcadj- taken place. The vesicle, which had increased v,ith. the growth 

 of the embiyo, has continued to enlarge over the surface of tlie membrane of the shell, 

 which now it entirely surrounds, thus forming an external co\-criug to the yolk. Tlie 

 large blood-\-essels ^\•hich connect the chick with this membrane — any one of which, 

 if left open, would prove fatal to the bird — begin to be sealed and shrink, and prepara- 

 tion is making for its escape. ' 



The position of the chick is such as to occupy the least possible sjiace. The head, 

 which is large and heavy in proportion to the rest of the body, is placed in front of the 

 belly, with the beak under the right ^^•ing. The feet are gathei-ed up, like those of a 

 bird trussed for the spit. The tij) of tlie upper part of the bill is supplied witli a tliick, 

 hardened, horny point ; and with this it makes a mark within the shell, tlius jjreiiaring 

 it to be broken. And though the position of the bird is singular, and a])j)arently 

 uncomfortable, it is by no means cramped or confined ; there is space enough for the head 

 and neck to acquire sufficient force to break through the shell and to cftect its escape. 



Tlio air-bag, placed at the large end of the egg, has often been noticed ; and the 

 question of its use as often debated. Mr. To\nie, of Guy's Hospital, has llirown much 

 valuable light on the process of incubation, and, in the course of it, on the air-bag, which, 

 curiously enougli, does not seem to vary in size, either with that of the egg or the liii'd. 

 He observed that tlie lining membrane of the shell was much changed during incubation, 

 and that, by the alterations that took jilace, ho could tell how far the process was 

 advancing successfully. 



The fiooi' ol' this reservoir of air, howcMcr, did not eluinge ; it remained thin and trans- 

 parent; and Mr. To«nic proved it to be a di.stinct membrane, unconnected witli lliat nt' 

 the shell. The use of this inner lining membrane, as he calls it, appears to be to hold 

 the contents of tlie egg suspended within the shell, and thus pi'otect the vgg from being 

 iiruiscd, which might otherwise happen, were the egg put in motion. It acts to tlic 

 • liick, in fact, as a natural hammock which the sailor has suspended for a resting-])lace 

 between the decks of a vessel ; thus tlii' little liird swings alung with the movements of 

 the .shell, and is effectually preserved from all injuiy. 



Hut what is the use of the air contained in this liag y 'i'lie answer of this most 



