546 ;' E. V. COWDKY 



of the human corpus luteum is lamentable. Corner (a) (e) describes the 

 conditions in the pig as follows: 



Mechanism of Formation. "In swine the membrana granulosa is re- 

 tained intact after the rupture of the Graafian follicle. Its cells increase 

 in size without division, their cytoplasm becomes laden with lipoid sub- 

 stances, and they become the larger elements commonly called 'lutein cells' 

 in the fully formed corpus luteum. The membrana granulosa is invaded 

 by blood capillaries from the theca interna, which ramify to form an ex- 

 tensive vascular plexus throughout the new structure. The large lipoid 

 laden cells of the theca interna are increased in number by mitotic divi- 

 sion, lose many or all of their fatty inclusions, and pass into the corpus 

 luteum to become lodged between the granulosa cells throughout the whole 

 structure. There is no evidence that cells of the theca interna are ever 

 converted into fibroblasts of the usual spindle cell type, or that they lay 

 down the fibrils of the close meshed reticulum which is present in the cor- 

 pus luteum. There appears to be good evidence that some of the theca 

 interna cells persist throughout pregnancy as distinct elements of the cor- 

 pus luteum, but it is not possible to learn by present methods the exact fate 

 of all of them, because of a confusing resemblance between some of the 

 theca and some of the granulosa derivatives." 



Retrogressive Changes. Both types of corpora lutea, the vera and 

 the spuria, undergo similar retrogressive changes. The yellow pigment 

 first disappears, the connective tissue contracts, and the corpora lutea be- 

 come reduced to the so-called corpora albicantia. These, in turn, decrease 

 in size until only fibrous vestiges, or corpora fibrosa, remain. Atretic 

 corpora lutea are formed, through the retrogression of Graafian follicles 

 which have not discharged their ova. 



Comparative Anatomy 



Conditions in Avians. The birds deserve special mention, because, 

 as Pearl and Boring have shown, contrary to what one might expect in 

 the absence of pregnancy phenomena, they possess, like mammals, typical 

 corpora lutea. The homology between the two seems to be very close; the 

 avian corpora lutea have the same general plan of architecture, are de- 

 veloped in the same way, and contain the same bright yellow pigment. 



]n birds it lias been shown by Goodale (d) that removal of the ovaries 

 causes the development of male plumage; hence the assumption is justified 

 that the ovaries, under normal conditions, produce 1 an internal secretion 

 which inhibits the development of these secondary male characteristics. 

 Boring and Morgan have discovered very striking evidence which confirms 

 this hypothesis in the sebrights, a race of birds in which the males are 

 normally hen-feathered. They have actually found cells in the testes of 



