144 DISEASES OF POULTRY. 



early stages of development of the chick the two ova- 

 ries are of equal size, but soon the developmental forces 

 appear to concentrate in the left ovary while the right 

 one remains stationary and ultimately disappears in 

 most birds. The single ovary is developed to a re- 

 markable degree. It is situated near the left kidney 

 and approaches the median line. The external ap- 

 pearance is that of a granular or nodular body attached 

 to the spinal column by a fold of peritoneum. The 

 nodules are irregular in size, some small and whitish, 

 others larger and of a yellowish color. 



The enlargement of the ovum is due to the accumu- 

 lation of the yellow or food yolk, and this causes dis- 

 tension of the ovarian capsule or calyx that encloses 

 the ovum. As the ovum enlarges its capsule becomes 

 more and more separated from the remainder of the 

 ovary until it is seen to be attached only by a narrow 

 base or pedicle. The calyx consists of two membranes 

 united by connective tissue and blood vessels. The 

 vessels converge towards a white transverse line or 

 band which crosses the most prominent part of the 

 calyx. At this line the vessels become so ininute as to 

 apparently disappear entirely. This band, called the 

 stigma, begins to appear when the ova are well devel- 

 oped and the line becomes broader and the membranes 

 thinner as the ovum increases in size, until at the 

 proper time the walls of the calyx give way along this 

 line and the egg slips out of its capsule and passes into 

 the infundibular opening of the oviduct. The empty 

 calyx collapses, rapidly shrinks and is ultimately ab- 

 sorbed. 



The ovum as it enters the oviduct consists of a 

 vitdlus or yolk enclosed in a very thin vitelline mem - 

 brane. Impregnation or fertilization occurs in the 



