58 Diseases of the Genital Organs 



uterus and an orange-colored corpus luteum and consider 

 the structure that of estrum. But there has been pregnancy 

 and the corpus luteum has not yet disappeared. 



The duration, or life, of the corpus luteum of pregnancy 

 presents a strong contrast in most domestic animals to the 

 corpus luteum of estrum. The corpus luteum of pregnancy 

 has as its minimum physiologic life the duration of preg- 

 nancy. The simplest cycle in ovulation, pregnancy, and 

 atrophy of the corpus luteum is in the rabbit where the dura- 

 tion of the corpus luteum and of pregnancy are identical. 

 The doe conceives, the corpus luteum forms, in four weeks 

 she gives birth to young, the corpora lutea have atrophied, 

 new ovisacs have matured and immediately after parturi- 

 tion she copulates with the male and conceives. 



In the cow, the corpus luteum forms promptly after con- 

 ception, attains its growth in seven to ten days and physio- 

 logically remains static until thirty to ninety days post par- 

 tum, or for a period of ten to twelve calendar months. 

 Pathologically (retained corpus luteum, pyometra, macer- 

 ated or desiccated fetus, etc.), the corpus luteum of preg- 

 nancy may remain static indefinitely and inhibit estrum and 

 ovulation. In the mare it appears that the corpus luteum 

 of pregnancy atrophies promptly after parturition so that 

 she is ordinarily in estrum at seven to nine days post par- 

 tum, thus giving it a physiologic duration of about three 

 hundred fifty-five days. In those animals which have short 

 periods of pregnancy and are normally in estrum semi-an- 

 nually, like the bitch, the corpus luteum appears to persist 

 for a comparatively long period after parturition or estrum. 



12. The Fetal Membranes 



After fertilization has occurred, the ovum passes through 

 the oviduct, propelled largely by the cilia of the tubal epi- 

 thelium, and soon reaches the uterine cavity. During its 

 tubal migration, the ovum has undergone segmentation. 

 The stored food material in the ovum is insignificant, so 

 that it must be dependent upon the uterus for any nutrient 

 material for the maintenance of life and development. The 

 nutrition of the ovum, embryo, and fetus is throughout in- 



