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CHAPTER IV. 



THE EGG AND SITTING HEN. 



EVERY animal, of whatsoever kind, is 

 developed from the egg-form, or as 

 physiologists express it, " omne animal 

 ex ovo." But the mode of that development 

 differs, in one detail especially. In mammalia 

 the egg is retained throughout within the body 

 of the mother, which is its sufficient protection, 

 and the development is uninterrupted. In 

 oviparous animals, such as birds, the egg is 

 enclosed in a hard protecting shell, and at a 

 certain stage of development extruded from 

 the body of the mother; in this case develop- 

 ment is arrested at that point, and may, or 

 may not, be resumed and completed. 



Fif». 21. — Ovary of Laying Hen, 



The ovary of a hen during or near her laying 



season presents an appearance much like that 



of a cluster of fruit, and is accurately shown by 



the illustration (Fig. 2i.) There 



Formation are, strictly, two such organs in 



every bird ; but one remains merely 



rudimentary and undeveloped, the 



fertile one being almost always that on the left cf 



of 

 the Egg. 



the spine, to which it is attached by means of the 

 peritoneal membrane. By the ovary the essential 

 part of the egg, which consists of the germ, and 

 also the yolk, is formed, each yolk being con- 

 tained within a thin and transparent ovisac, 

 connected by a narrow stem or pedicle with the 

 ovary. These rudimentary eggs are of different 

 sizes, according to the different degree of de- 

 velopment, and during the period of laying 

 they are constantly coming to maturity in due 

 succession. 



As the yolk be- 

 comes fully matured, 

 the enclosing mem- 

 brane or ovisac 

 becomes gradually 

 thinner, especially 

 round its greatest 

 diameter or equator, 

 which then exhibits a 

 pale zone or belt called 

 the stigma. Finally, 

 whether or not fecund- 

 ation takes place, the 

 sac ruptures at the 

 stigma, and the 

 liberated yolk and 

 germ, surrounded by a 

 very thin and delicate 

 membrane, is received 

 by the funnel-shaped 

 opening of the oviduct 

 or egg-passage, whose 

 office it is to convey 

 it to the outer world, 

 and on its way to 

 clothe it with the 



other structures needful for its development 

 and preservation. This organ, with its various 

 convolutions a little modified for convenience 

 of representation, is shown in Fig. 22, and 

 in an ordinary hen is nearly two feet in 

 length. It will easily be seen how tivo yolks 

 may become detached and enter the oviduct at 

 nearly the same time ; in which case they are 

 likely to be enveloped in the same white and 



Fig. 22. — Ovary and Oviduct. 



