CHAPTER VIII 



THE PERIODICITY OF (ESTRUS 



{a) ROLE OF THE CYCLIC STRUCTURES OF THE OVARY 



The intimate correlation between the cyclic changes in the 

 ovary and those in the accessory organs naturally led to the 

 conclusion that the periodic development of the cyclic structures 

 of the ovary was responsible for the cyclic changes in the 

 accessory organs. At first considerable attention was given to 

 the corpora lutea as the main regulators of oestrous periodicity; 

 it was held that their development after each ovulation inhibited 

 a further appearance of oestrus during their functional lifetime. 

 This view was supported by the various experiments in which 

 the removal of the corpora lutea was found to expedite the 

 appearance of the following oestrous period. There are many 

 reasons, however, for concluding that oestrus is not necessarily 

 preceded by the atrophy of corpora lutea. (a) The appearance 

 of oestrus at puberty or after anoestrus occurs when no corpora 

 lutea at all are present in the ovary, (b) In many animals the 

 atrophy of the corpus luteum at the end of pregnancy is not 

 followed immediately by oestrus (rodents, of course, are an 

 exception to this). It may be concluded, therefore, that while 

 the corpora lutea, when caused to persist, undoubtedly have 

 the effect of delaying the next oestrous period, they do not 

 regulate the essential periodicity of oestrus. It follows that 

 if any cyclic structure of the ovary has this function, it 

 must be the mature Graafian follicle, and many observations 

 tend to support this view. 



{b) RELATION BETWEEN THE GRAAFIAN FOLLICLE AND 

 THE PRODUCTION OF CESTRUS 



Functional correlation. In the normal animal a regular 

 connection is found between the maturation of Graafian 



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