o 
6 
CHAPTER IV. 
EGGS AND INCUBATION. 
The motto “ omne animal ex ovo,” adopted by the New York State Poultry Society, aptly 
expresses a truth well known to all physiologists. All real animal life is developed from the egg- 
form ; the only difference consisting in the mode of development, which in some cases is entirely 
completed within the body of the female, whilst in others more or less of the process is carried 
on after separation from her. It is in these latter cases that some kind of hard case or shell 
becomes obviously necessary for the protection of the egg until the embryo is ready to commence 
its active existence ; and as in the case of birds we find the whole egg-structure in the most 
perfectly organised form, it may be proper to give a very short and popular description of 
its formation. 
Fig. 1 6 . 
The ovary of a hen during or near her laying season presents an appearance much like that 
of a cluster of fruit, and is very accurately shown by the illustration (Fig. 16). There are more 
properly two such organs in every bird ; but one remains merely rudimentary and undeveloped, 
the fertile one being almost always that on the left of the spine, to which it is attached 
by means of the peritoneal membrane. By the ovary the essential part of the egg, which con- 
sists of the germ, and also the yolk, are formed, each egg being contained within a thin and 
transparent ovisac, connected by a narrow stem or pedicle with the ovary. These rudimentary 
