The Corpus Luteum of Estrtim 53 



the ovary draws over the naked granulating surface until 

 at seven to ten days, the structure, if physiologic, has lost 

 its central cavity, the blood coagulum has disappeared and 

 the epithelium of the ovary has recovered its continuity. 

 The corpus luteum of the cow is then five-eighths to three- 

 quarters of an inch in diameter, usually spherical or ovoid, 

 but subject to numerous variations, has an even contour 

 and is firm in consistence. It is readily recognized in the 

 cow by rectal palpation and usually easily dislodged by digi- 

 tal compression. If the ovum discharged is not fertilized, 

 or if the fertilized ovum perishes quickly, the corpus luteum 

 of the cow is not yellow but with great uniformity is choco- 

 late or liver-colored. Its size, contour, and consistence are 

 essentially the same as in pregnancy. The volume remains 

 virtually constant after its growth has been completed at 

 seven to ten days until at a period of about three or four 

 days prior to the maturation of the next ovisac, when it 

 commences to atrophy rapidly, and when about one-fourth 

 inch in diameter, a new ovisac ripens, generally in the oppo- 

 site ovary, the animal is again in estrum and ovulates. The 

 old yellow body has permanently ceased, so far as known, 

 to exert any influence upon the reproductive processes. It 

 continues to atrophy slowly. There are frequently visible 

 in a single section in the ovary of the cow, three to five old 

 corpora lutea, one-eighth inch or less in diameter, with 

 white strands of connective tissue scattered amongst the 

 nests of lemon or orange-colored lutein cells. 



6. Copulation 



The male ordinarily exhibits little or no sexual desire ex- 

 cept in the presence of a female in estrum, but the testes 

 function constantly. The sexual desire may be activated 

 at any time when a female in estrum approaches sufficiently 

 near to be recognized, and copulation occurs when opportu- 

 nity offers. 



During the act of copulation, the semen from the male is 

 ejaculated into the vagina of the female, possibly in part 

 into the cervical canal. The semen has as its essential con- 



