CORPUS LUTEUM IN OVARY OF THE CHICKEN 11 



111 the third oldest corpus luteum, the tissue is shrunken so 

 that a mere speck shows on the surface. This is the stage re- 

 sembhng the yellow spots of the hen's ovary. Dissection shows 

 that it is reduced in all diameters. That part of this decrease 

 in size is due to cell shrinkage is well demonstrated by com- 

 parison of figures E and F, which are drawn to the same scale. 

 Not only the nucleus but the cell body is at least halved in 

 size. The color now is darker, being a brick red. This is not 

 due to blood vessels, as sections do not show any more than 

 formerly. It is due to the development of a dark yellow pig- 

 ment, the same substance which appeared in small quantity in 

 the younger corpus luteum and in large quantity in the hen 

 ovary. In this stage of involution it is developed in large quan- 

 tities, practically fiUing up many of the lutear cells (figs. 19 and 

 21 and fig. F). In unstained sections it gives a yellow color to 

 most of the section. 



In the fourth oldest corpus luteum of the two series and in 

 the scattered older ones sectioned, the structure is similar to 

 that in the third oldest, the yellow amorphous masses being 

 possibly larger and more distinct. 



This yellow material certainly looks the same as that in the 

 hen ovary. The chief structural difference is that it is all con- 

 fined within cells with distinct cell walls in the cow, while in 

 the bird, the cells forming it, lose their boundaries and the 

 particles are formed in a vacuolated network with scattered 

 shrunken nuclei (cf. figs. 20 and 21). 



Sudan III reacts similarly with hand sections of formalin 

 material from both cow and hen ovary. All four stages in the 

 cow series take the red color showing the presence of a fatty 

 substance in the cell. This corroborates the evidence from 

 the solvent action of absolute alcohol and xylol. But in the 

 third and fom-th stages, yellow amorphous pigment particles 

 can be seen glistening in the red background. The pigment is 

 not of fatty nature in the cow, any more than it is in the hen. In 

 fact, this substance is so similar in the two animals, that we 

 shall from now on speak of a corpus luteum in the hen, and call 

 the cells forming this pigment, lutear cells. 



