168 GEORGE W. CORNER 



the pressure of the many neighboring corpora lutea of the same 

 crop, until there is produced a knoblike hernia of corpus luteum 

 tissue sometimes containing a tenth or more of the whole corpus 

 luteum (fig. 20). This appearance is sometimes called by the 

 handy German name 'Pfropf.' In some species, as, for instance 

 the cow, it seems to occur invariably and to persist throughout 

 pregnancy, but in swine the hernia is not always produced, the 

 whole wall of the corpus distending evenly instead; and later it 

 seems to subside, as in most corpora lutea in more advanced 

 pregnancy there are no 'Pfropf en.' 



THE FULLY FORMED CORPUS LUTEUM AND ITS MORPHOLOGICAL 

 CHANGES UNTIL THE TERMINATION OF PREGNANCY 



Invasion of the granulosa by the thecal vessels and cells begins 

 about the third day after the onset of oestrus (or about the sec- 

 ond or third day after rupture of the follicle) and is completed 

 about the sixth or seventh day. My series contains five sows 

 killed during the second week after ovulation and a large num- 

 ber from all stages of pregnancy from fifteen days after ovula- 

 tion on to full term and into the period of lactation, so that 

 altogether there is an unbroken series representing almost every 

 day of the entire reproductive cycle. 



By the seventh day the corpus luteum may be considered to 

 have completed the first stage of its metamorphosis. It is solid 

 (unless there has been a decided haemorrhage into the cavity), 

 and it is already larger than the follicle in which it arose, reach- 

 ing diameters of 8 and 9 mm., although a slow increase in size 

 is yet to go on until the second or third week, by which time the 

 full diameter, 10 to 11 mm., is reached. The blood-vessels 

 have grown into a very narrow-meshed plexus, reaching every 

 cell. The remains of the former great folds of the walls are seen 

 as thin septa of connective-tissue fibrils running radially into the 

 corpus luteum, carrying the larger blood-vessels of the organ. 

 In some specimens, just inside the theca externa capsule and 

 along the septa is a layer of theca interna cells or sometimes a 

 few scattered clumps of them which have not chanced to in- 

 vade the granulosa. These clumps may be found as late as the 



